ICS, games online, and Symantec

I have symantec firewall running and I have gotten it to work with games just fine. The exception is playing online through the modem on one of my computers. The game on the computer with the modem connects just fine. But when the same game on a different computer attempts to connect to the Internet through my computer with the modem, it is not able to get through correctly. When I disable Symantec, it works fine. Local LAN games work fine as well.

<font color=red><b>NF7-S/MBarton 2500+
210x11.5 1.82v SP-97
GB Corsair XMS PC3200
BBA 9800 Pro 423/369</font color=red><font color=black>
NF7-S/MBarton 2600+
210x11.5 1.76v
512MB CVR PC3200
Sapphire 9500@9700