I remember a friend of a friend of mine
being in a similar situation.. Not with XP tho. If you copy and paste the XP "Windows" directory from one comp to the other and run the upgrade on the new one, one would think it would work.
I am presuming u just have the 98 "floppy disk"? Not the actual CD right?
EDIT: or it might complain about it being the same version and might ask u to "repair" the install instead.. Try anything they suggest and see what happens