If you're attempting to run a gnutella client behind a firewall (such as from a school), in all likelihood, the default gnutella port is blocked (port 6347).

You may try to "sockisfy" your gnutella client, using SocksCAP or Socks Hummingbird. This converts all IP/UDP calls to SOCKS. Then you can use Socks2HTTP to convert the Socks packets into HTTP packets, which will traverse your firewall on port 80. You'll need to have port 80 open through the firewall for your computers, which is probably the case, as most schools allow web surfing from all workstations.

Hope that helps.