You have to try it, that is the only way.
Now, if UPnP works then you will not have to "Port Forward" but, because of the way different manufacturers implement UPnP, most people have found that they have no choice.
As you know what you are doing, follow these instructions:-
a) Implement IGD in XP
How to enable IDGC on WinXP SP2.
http://www.gnutellaforums.com/connec...tml#post292985
b) Implement UPnP in your modem, Limewire and XP
c) Turn off "ICMP" in your modem and your firewall, if it is there.
Once you have done all this (and saved the changes) do a reboot to get the changes into memory and see how things work out.
Good Luck
UK Bob