Mechwarrior 4: Vengeance MP problems (maybe OS?)

Hi, I have a few computers computer that I have on lan, all completely
capable of running Mechwarrior 4, only two share a common operating
system. I can't cannot connect my computer running on XP to games that
are running under windows 98, is this a correct observation or is
there something else that might be prohibiting me from connecting.
I've tried reinstalling and they all are patched.

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