Try this, it worked for me;

1. Open up 'System Preferences'
2. In 'Internet & Network', open 'Sharing'.
3. Select the 'Firewall' tab (your Firewall should be on)
4. Select 'New...'
5. From the 'Port Name' drop down box, select 'Gnutella/LimeWire'
6. Select 'OK'
7. Restart your LimeWire application.

Oh, and this is for users running Mac OS X version 10.4... If you're not running this then you'll have to do a little more digging =/

Good luck and hope you all get Limewire running soon ^_~