I've been using the MS P2P software in their program threedegrees, and it's been very stable, and when combined with their IPv6 stack, I've had no problems communicating with other people in a variety of different firewall situations.

Will someone use the newly released P2P SDK and work it into a Gnutella client? I think that the results will be pretty interesting...

http://msdn.microsoft.com/library/de.../winxppeer.asp