Huh.
I'd suspect that XP must use one anyway then, like Tom said. I'd guess all the user does is decide if it stays on the same place on the disk. I'm sure they have their reasons for insisting upon it's use so it's probably a cost of doing business with MSW.
My experience with this subject if fairly limited and I've reached the end of it. If you have the time tinker, google and repeat till you get a sense of it. Otherwise I'd forget about the whole thing... :)