They have probably blocked the gnutella port. In fact, they have probably blocked all the ports except those for HTTP (port 80) and maybe one or two others.

If they have only blocked the gnutella specific port - then you should be able to change your port - see:

Tools|Options|Advanced

for changing your default port.

But your message suggests that they have blocked a whole host of ports (indeed it is often easier to specifically open the ports you want than to close the ports you don't want).

If this is the case then there isn't a lot you can do about it (unless you can find some ports they've left open - they will have left 80 open and perhaps 21, but these have other uses - use at your own risk).

Mark