For all my googleing it appears the best you can do is tell your computer not to use DHCP; I cannot find a way to do this at the Access Point level.
EDIT: This is not for port forwarding. This is for an internal mythTV server. Right now the DHCP server on the AP is set to assign IP's from 192.168.1.100 - 192.168.1.149. When I set a static IP outside that range on the computer that computer is unable to connect to the Internet.
I've done this before on my old Buffalo brand AP (may it RIP) without any problems. This seems to be a WRT54G2 specific issue.