I can't tell you a thing about XP so I'll just mention that a reg backup on this w98 machine shows about 6MB.
Perhaps a XP user will post and tell you whether your in the ballpark or not.
I just backed up my reigistry and was surprised that it would not fit on a floppy. Ended up using a 100 meg zip disk. The registry back up was 52 megs. Does that sound right? xp pro, p4 2.2 with 512 megs rambus.

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