if xp was reinstalled then the security credentials will be different, so you wont be able to access them
if its a folder, right click on it then properties, click on security tab once the property tab comes up, once the security tab comes up, click on the owner tab
here click on your current user and make sure "Replace owner on subcontainers and objects" is ticked
click on ok and then yes to all till it finishes
that should let you have access again