venomlash 55 Junior Poster

I have a POS Dell Dimension 4600. It recently went into Krakatoa mode (i.e., whenever I try to start it up it <explodes>). The Windows XP system we had on there proved to be beyond repair (whenever we try to "repair install" the blasted thing just reboots repeatedly until shut down), so we had to install a new OS alongside the old one.
Here's the biggest problem: me and my sister's documents were declared "private", meaning only our users could open them. Now, those documents are inaccessible because our new users are different from the old ones with the old OS. How do I break the "access denied" message and get my files??? HALP!!!1!