There are two possible explanations
1. You've got more than one windows XP cd and installed using the wrong one.
2. You weren't running XP 64 to begin with
XP 64 won't (and can't) just revert back to 32 bit windows XP.
Originally Posted by peterhuang913
your screen jilts when you scroll because the vid drivers are not up to date or its running on VGA default
I don't think that's what he was talking about.