Online game trouble.

I'm not sure if this is the right forum but here is my problem. I have 2 computers on my home network one with win98 and one with xp and linksys
router. My son plays this online game called robot rage where you build a robot and battle other robots. The computer with xp works fine but the one with win98 will do everything except battle other robots. The game tells me I am behind a firewall which I am not, unless it is in the router. If thats it then why does the other computer work fine. Both systems are using intel pro/100 cards and all settings are the same. any help appreciated

thanks wes