Some ISP's do block Gnutella traffic....
If you're running Windows, you can perform the following test to see if you can connect to Gnutella. If you're not Win.... you can still run the test if you know where to find the telnet program on your OS.

1. From the Start menu, choose "Run".
2. In the dialog box, type "telnet 64.61.25.171 6346". Click OK.
3. A window will appear. If it doesn't say "GNUTELLA OK" within a few seconds, your ISP is probably blocking Gnutella traffic. If so, there's not much you can do about it.

Good luck.