Which firewall? Windows XPs? Hardware? The firewall is like a bouncer with a list of names of people who can get in. If your not on the list... To get in the bouncer needs to know who you are (ie program name) and how you will arrive (which "port"). So you might have Limewire using port 6997 via UDP or TCP. PnP is a system that looks for someone who is waiting for a connection and is more automated.
To get through the firewall the firewall application must know which port Limewire connects with. I generally pick an easy number (eg. 12345) and set Limewire to use that (using the preferences in Limewire). Then for software firewalls like the windows one you create an exception. It will need to know the program (c:\path... Limewire\limewire.exe and the port number it is using. I believe u need to add two port settings, one for UDP and one for TCP.. use the same number for both.
If it is a router you are using you may need to try using PnP to automatically get through the modem or if this isn't available youi need to learn about port forwarding.
Contact me if you are still stuck!
Mart9012
June 2007