Pick a number like 64049. Sometimes isp's don't block the ports in that range. It's pretty much a shot in the dark. Here's some others to try: 1111, 3500, 4008, 1203, 80, 20282, 10000, 443, 40475.
In case your wondering, I got those numbers from this thread:
http://www.gnutellaforums.com/showth...14&#post179814