I just noticed you had this same problem previously with Windows XP on different machines,
http://www.gnutellaforums.com/connec...tml#post352579
From what I have learnt since then, at least for my router brand it is possible to port forward and run UPnP at same time even for same computer but different ports and applications.
Something else I have learnt more about since then is the unreliability of wireless networking and UPnP. Too many connections and the wireless system struggles. Using LW usually results in lots of connections albeit indirectly with spam hosts and the like pinging your client.
Are you still using a AT&T 2Wire Router?