Despite the connections, Xenophon's dialogue is very different from Plato's. While eros is also thematically important here, he takes things in a very different direction. It is also a more humorous dialogue, and despite its clear anachronisms, a more realistic dinner-party, as people enjoy the entertainments, get rambunctious and occasionally goofy, over-drink, and get annoyed at each other. Plato gives us after-dinner speeches; Xenophon gives us a party, complete with a dancing Socrates.
You can read Xenophon's Symposium online in English at the Perseus Project or Project Gutenberg.
(in order of appearance)
Xenophon opens by claiming that he witnessed the events in question, but he does not actually participate in any of them. (And it has been noted more than once that he is one of the anachronisms of the dialogue; he would have been less than ten years old at the time the dialogue takes place.)
Callias son of Hipponicus
Callias is hard to summarize. He would have been extremely well known to anyone in Athens, being the wealthiest in all of Greece (with his father the wealthiest man in Greece before him), and actively involved in politics. Because of his extraordinary wealth, he was repeatedly required to fund liturgies and warships by the city of Athens (the Athenians had no regular taxation, since they covered anything not already covered by tribute from their empire by requiring wealthy citizens to pay for them, a fact noted with some ire in this dialogue by Callias himself). He repeatedly is mentioned in comedies and did not have an entirely savory reputation, being something of a regular scandal-magnet. He is the same Callias who holds the sophists' get-together in Protagoras, and his connection with the sophists is explicitly referred to here by Xenophon, as well. He was related on his mother's side to Pericles and Alcibiades and through his first wife to Plato.
Autolycus is mentioned here at being the pancratist winner in the summer of 422. (The pancratium was a mixed martial arts event in which one could use any means to defeat the opponent except biting and gouging.) He is mocked by comedians like Aristophanes for dissolute behavior. An outspoken democrat, he was eventually murdered by the Thirty Tyrants.
Autolycus's father. This is almost certainly the same Lycon who with Anytus and Meletus would later bring charges against Socrates. There is nothing in Xenophon to indicate that he was even aware of Lycon's role (Xenophon had all his information about Socrates' trial secondhand, since he wasn't in Athens at the time), but if he was, it makes his parting comment to Socrates extraordinarily poignant. He was of some influence in Athens, and had a reputation for extravagant living despite his poverty.
Niceratus is the son of the Nicias who is a character in Laches. He is one of the anachronisms of the dialogue, since he would have been too young to be wed at the time the dialogue took place. He would be executed by the Thirty Tyrants.
Critobulus is the son of Socrates' close friend Crito.
Hermogenes is Callias's half-brother, but he was illegitimate and as poor as Callias was rich. Plato's Cratylus, in which he is a character, mentions that he saw Callias as having cheated him out of his inheritance. He shows up a lot in Xenophon, since he is apparently Xenophon's source for Socrates' last days.
Antisthenes is one of the more important students of Socrates, because he formed his own school, and his thought is generally thought to have been an influence on the later Stoic and Cynic movements. He was wealthy, but he seems to have made a point of non-attachment to possessions. Xenophon portrays him as quite volatile.
Charmides is Plato's uncle, and, of course, a character in Charmides. He was one of the ones accused of illegal performance of the Eleusynian mysteries at the time of the sacrilege of the herms, and as a result was sentenced to death in absentia. A firm oligarch, he was a close associate of Critias's and would become a member of the Ten who governed the Piraeus under the Thirty Tyrants.
Philippus is known only from Xenophon; he was a clown or comic, getting invited to dinners by joking around at them.
In addition there's a Syracusan with girls and boys who are dancers, reed-players, and the like.
The Plot and The Thought
After the horse-races at the Great Panathenaea, Callias is walking home with Niceratus, Autolycus, and Lycon when he comes across a group consisting of Socrates, Critobulus, Hermogenes, Antisthenes, and Charmides. He invites them to his dinner-party. Socrates actually remarks that he must be teasing, and all the others try to beg off, but it is clear that if they don't attend he will be quite annoyed. They all go to Callias's house and start eating in silence when Philippus comes uninvited and tries to get in; Callias decides to let him in, and Philippus tries to crack some jokes, unsuccessfully. After dinner they pour libations to the god and sing a hymn, and then the Syracusan comes in with two girls and a boy for the entertainment. After listening to the music of reed and lyre a bit, the conversation happens to turn to the question of whether true goodness can be taught. Socrates refuses to discuss it (compare Meno), but as the entertainments progress repeatedly makes comments that together constitute an argument that it can be taught. Note also Socrates' explicit statement that women are capable of education -- a more controversial claim for the highly misogynistic ancient Greeks than it would be for us -- and that women can be taught the virtue of andreia, which is translated as 'courage' or 'fortitude', but in the Greek means 'manliness'; the claim that women can even have the virtue would have been highly paradoxical to the ancient Greeks. Obviously, if women can have the virtue of manliness it follows directly that virtue can be taught, since they wouldn't be manly by nature.
Socrates asks the Syracusan if he could teach him to dance; and when everyone laughs, notes that Charmides came in on him dancing that very morning, which Charmides confirms. Philippus gets up and parody-dances. They start drinking, following Socrates' suggestion to have lots of little glasses of wine rather than a lot of wine all at once. They go around the room stating what they are most proud of. Callias says his is the skill of making people good with money; Niceratus's skill is being able to repeat all of Homer by heart; Critobulus's is being good-looking; Antisthenes's is wealth, despite having very little money; Charmides's is poverty;Socrates says that his is mastropeia, which is (more or less) the trade of pimp; Lycon says his son Autolycus; Autolycus says his father Lycon; and Hermogenes says it is the goodness and influence of his friends.
Having stated what they're most proud of, they then have to give their reasons. They do this with most joking. The most significant of the arguments are Critobulus's argument for good looks (which sets up a later stage of the dialogue, since ugly Socrates challenges handsome Critobulus to a beauty contest), Antisthenes's speech that wealth is all in the mind (which seems clearly to be an indirect attack on Callias, although Callias doesn't seem to be too riled by it), Hermogenes's argument that his friends are the gods, and, of course, Socrates' argument that he is an expert at pimping or sexual procuring. Socrates' argument is that what he does is to set up handsome young men with minds to teach them; he ends by conceding that straight-laced and ascetic Antisthenes is a better pimp than he is.
Socrates and Critobulus then face off in the beauty contest, judged by the musicians, with Socrates arguing that he is, in fact, more beautiful than Critobulus. Critobulus wins, of course, and Socrates accuses him of bribing the judges. The conversation lags, although Socrates manages to get it going again (it's notable all the way through that almost all of the actual conversation is due to Socrates; Callias himself, despite his training under the sophists, doesn't seem to be any good at keeping the discussion going). The Syracusan, however, notices that the guests are paying more attention to each other than his entertainments, and insults Socrates. (The Syracusan's view of Socrates is taken directly from the way Socrates is portrayed in Aristophanes' The Clouds.) This threatens to get out of control very quickly, since Antisthenes immediately jumps to Socrates' defense, but Socrates defuses the situation masterfully.
Socrates then begins a discussion of eros that is worth comparing with Plato's Symposium. If Xenophon's Symposium was written after Plato's, a good deal of this speech is a vehement attack on the speech of Pausanias, whose claim that pederasty was a higher love than love of man and women Socrates attacks as a defense of wallowing in license. The overall theme of the argument, however, is that eros for beauty of mind is greater than eros for beauty of body.
Lycon and Autolycus leave, with Lycon saying that Socrates seems to be a truly good man, and then the Syracusan's troupe does a little play about the love of Dionysus and Ariadne. It's a fairly intense little production, and has the married men all going home to sleep with their wives. It's a little difficult to know what to make of this; but one way of reading it is to take it as showing that no one has actually learned anything from Socrates' argument. Socrates and some others set out with Callias for Autolycus's house, and so the dialogue ends.
A major theme of the work as a whole is found in the very first paragraph:
It seems to me that in writing about the deeds of truly great men, it is proper to record not only their serious activities, but their diversions too.
The intermingling of spoude, earnestness, with paidia, playfulness, is repeatedly mentioned in the dialogue. Thus Xenophon is showing that philosophy involves a kind of play (paidia) as part of its teaching (paideia) of virtue.
Quotations are from Xenophon, Conversations of Socrates, Tredennick & Waterfield, translators, Penguin (New York: 1990), pp. 219-267.