sorry to not contribute anything helpful, but i too have a WRT54G and have only recently not been able to host. i'm not sure when it happened, since there was a long period when i didn't have any need for forwarded ports, and when i finally did i found that it just wasn't working.

i've tried pretty much every solution out there to no avail. i had AVG installed, but uninstalled it out of sheer paranoia, and i've already made sure there are no other firewalls up (such as the default windows firewall). i am, however, suspicious that my modem could be acting like a router, causing the ports to get blocked there (called something along the lines of a double NAT?)