Does Any Jabber Client
 

Support file transfers to and from AIM and Adium/iChat accounts?

That's not really up to the client to support, but rather it's the server's AIM gateway that has to support file transfer. From my experience with the MSN gateway it sometimes works and sometimes not, even with the same version gateway. You really need to find out who makes the gateway for your jabber server and ask them if they can implement it.

Okay, if it's not a client side facility, can someone give me the name of some Jabber servers that (a) have transports to all the Big 3 IM providers and (b) allow file transfer from at least AIM and MSN.