I've not used activex controls much so bear this in mind with my advice.
On the Win 98 computer you found the activex control because it is installed, possibly when Foxpro development was installed or from some other program. You could install Foxpro on the XP computer, that should fix it. As far as I know you can register it without Installshield. Look at the beginning of this thread for code on how to do this. Keep in mind, I have not gotten this code to work. If you have any luck with it let me know.