Regarding the firewall I use the Sygate firewall

http://www.gnutellaforums.com/showthread.php?t=58498

It's the last freeware version of it, but really good.

Antivirus AVG free (not that good but still better than nothing :wink:)

And Ewido antispyware (Good but kind of a resourcehog)

What all of these have in common are that they're free and do not interfere with Limewire (Sygate of course needs to be configured but is very userfriendly and easy to set up)

If the test works then it's probably not the ISP blocking anything

One option that's left is that you talk nicely to the administrator and ask him if he could forward a port for you (one of the high ones mentioned in the threads above) for both incoming, Outgoing, TCP and UDP. This problem is almost certainly caused by some security measure implemented by your administrator (knowingly or not). Forwarding a port would override all other rules in his system usually. I'm not that knowing of big networks so there may be needed other things to be done, but if he's good at his job he should have no problem figuring this out.