Well make sure all of your discks you got from Dell are handy. You wont need all of them just the ones that are for OS, Drivers. If you got any software that you would like to reinstall have that handy as well. The easiest thing to do is restart your computer, when you see the BIOS screen hit F2 to enter setup and make sure you can boot from CD. Save changes and make sure you OS CD is in the drive and let it boot. Hit a key when it tells you. Just follow the instructions form there. If you see that it has a huge partiton for nothing you can just delete all partitions and create new ones (or dont create any at all) then just format the drive and install XP. It is kinda self explanitory but if you want deep instructions i can give them just ask.