Just recently changed over to dsl again from cable, and have the same exact 2Wire unit from BellSouth/AT&T. Having the same firewall problem, but got mine working from the PF.com doc Remoc linked to. I tend to forget about PF.com from time to time, it's been a huge help with xbox360, ps3 and pc dilemmas, thanks for the link Remoc, Rep up'd!
Hopefully the OP has since gotten their problem resolved as well..if not, make sure that the manual port # and the listen on port # are the same, just for the sake of eliminating variables when setting the firewall rules on the 2Wire.
Oh yeah, this is my first post on the boards, guess now I feel obligated to go introduce myself properly!