Are both machines accessing the internet through the router or is your 98 machine going through your XP box to connect? If it is, do you have the default firewall on the XP box turned off?
Second, do you ever have this problem when downloading large files or doing anything else that requires a persistent connection? Do you ever get disconnected like this from other servers when playing on one of these two machines?
And finally, when you host on one machine and play on the other, do you have the problem or does it just affect folks coming in through the router?
------------------
"If your philosophy does not produce corn, I don't want to hear about it." - Red Bear