Networks Replacement for MS ISA on 2003 Server

Hi there, my routers port forwarding died a death. Tried firmware and reinstalls but nothing. So im building an ISA server. But ISA is expensive... And im poor, well im 16 so thats speaks for itself. So does anyone know of any other software MS based (iv tried coyote and smoothwall, they dont like just one NIC and being in a DMZ.)

All i need it to do is portworwarding to internal addresses. It will sit in my routers DMZ (still works) and then forward all traffic to where it should go. This traffic being web server on port 80 and web mail on 3000 ftp etc etc.... maybe a HL2 server. but i dont know. All these on different Machines so i cant just put the server in the DMZ.
Also a web config interface would kick ass too.
Thanks.
Ben