It really sounds like your ISP is at fault here. Try googling them to see if anyone else is having trouble with them as well.

You are sure that you do port forwarding right, right?

There should be no reason to forward anything else, than the port you use as listening/forwarded port, in your router. And in your software firewall allowing Limewire.exe should be enough.

What software firewall do you use BTW? You could try removing the rule about Limewire and readding it.

Also what version of Limewire and Java do you use?