start>control panel>systems
On the tab at bottom should be listed your w7 product key, its with mine. You should be able to use that key with any fresh install of windows, keep your name associated with it. MS will look for multiple installs with that product key, as long as its the only active unit you should be alright. Or you never try an update or activate.
With that product code, you can use any install disc. At least I was able to use a single XP disc with 2 pc, separate id's............................ ...I had purchased 2 separate discs, 1 became damaged, kept the product keys.
luck