How did you back them up?
Using the Files and Settings Transfer wizard? Or by dragging files off onto disc or something?
If it was using the Files and Settings Transfer wizard. you should be able to run this again in Start, Accessories, System Tools, and select that you are on a New Computer, and then put the disc in or where you saved them to, and it should restore.
If you just dragged files off, like for instance from documents and settings, just drag these back as they'll be fine.
If you for instance dragged off program files that might have had links to the registry though, you might have a problem, and will have to install them again
Hope this helps