RAS setup with multiple modems, cant browse the internet

Hello,
I have windows 2003 server as our domain server and had setup the RAS with three modems to have dial up access to the office. Right now, only the first incoming connection can browse the internet, the rest of the dial up PCs have all the ports closed, only Terminal Server access is available. Why is this happening? All ports in the RRAS are configured the same, they get the proper IP, gateway and mask…but only the first connection works.
Any ideas? We have posted this at MS newsgroup in several ocassions without an answer, also contacted the MS Concierge and he suggested to have MS support contacted for a fee.
tia,
Lizet