If you can't or don't know how to change firewall settings, LimeWire can circumvent it. Go to Tools > Options. On the Advanced tab, there is a section called Force Local IP. Check the Force IP checkbox. Manually enter in your IP address and force to port 6346 or whatever port you normally would want to use.

To obtain your IP, go to one of these sites. Alternatively, you can click Start > Run, type winipcfg and hit enter in Win 98 or download a small internet utility such as StayAlive Pro.

http://www.lawrencegoetz.com/programs/ipinfo/

http://www.aws.com/support/faq/software/ip.asp