I'm looking for a good p2p program for transferring files over a LAN preferably one that works over multiple operating systems. Any suggestions?
You might try DC++, I hear it works quite well in a LAN-party situation.
p300 from http://p300.eu/ is a free, open source, cross-platform (Windows, Linux, OS X) LAN-oriented file sharing tool.
waste is a highly secure solution. Development has stalled, but the current version works great.
@Blorgbeard DC++ is nice, but it's not really what I'm looking for because it requires a hub.
I don't really like DC++, because it requires a lot of hashing before it works. Even with modern high powered machines, big sharers need to hash for a very, very long time, and during this time their machine lags and is unable to do anything like gaming.
Hashing 1000GB+ on a a single core takes about a day, so unless everyone hashes in advance, a lot of precious leeching time will be lost.
I've not used p300 myself but it looks very promising.