Not sure what your intent is in disabling simple file sharing, but if
users are using XP Home Edition or XP Pro with simple file sharing, they
can make their documents private, which requires the account to have a
password, with just a checkbox, which I think satisfies the OP's intent.
Otherwise, if they disable simple file sharing in XP Pro, as you
suggest, they have access to all permission settings and the attendant
complexities of learning how to use them.
But I probably missed something in your direction.