Limewire can run with firewalls!
you just have to open the port (6346) for limewire to run. no application can run if the needed port is not open.
i don't think proxying is supported by any recent gnutella client.

in limewire you can set the force IP function which in case of a firewall helps others connecting to you. but you still have to open up the right port.
does morpheus run in your office???
if so try gnucleus it's free and gnutella like morpheus was just forked off of it.
http://www.gnucleus.com

mahalo