Sorry I missed your reply somehow.
Something I learnt about the 2Wire routers a day or two ago is you can allow applications per computer through the router's NAT firewall.

Check this post http://www.gnutellaforums.com/371489-post91.html This 'might' be the problem. (similar problem of no p2p apps connecting.)
You will probably need to find the address of your computer's network address. Here's one way http://www.markacadey.net/go/myip/ using ipconfig command.

This might be why only one computer is connecting with these applications. Your new computer might have a different network address to the firewall allowance(s) that is already there.