Rather than disabling the firewall (make sure you're only using 1), better to configure it properly.
Firewall setup

Do this test & see whether it works
http://www3.limewire.com:6346

Have you tried using p2p apps before & if so, did they work?

Have a look through the thread below. If your port test doesn't work, try changing to a higher port as suggested by LOTR. Also check out his link to "Connection problems...check here first".
http://www.gnutellaforums.com/showth...274#post189274

If you're still stuck, post back with your details (excuse any repeat questions!)

OS(Win XP etc)
LW & Java version (help > about LW & you'll see)
Firewall you're using
Modem/router brand & model
ISP
Connection type (DSL etc)
Where you connect from (home, school etc)
Are you sharing a connection with other computers
Is this your first try with LW