I've never done this but you should be able to simply re-install XP from disk normally. You'll be asked if you want to repartition & re-format. I would do so and that will be the end of W7. The rest should be a normal XP install. Alternatively, you can always install XP in a second HDD and use the W7 drive to migrate data when finished. BTW, XP is schedueled to be supported through 2014, I believe.