IF you are truly a Dual Boot System, when you boot your system it will give you a choice of Mandrake or Other. If this is the case and you do not want to reinstall XP and its gazillion updates. Format the drive that contains Mandrake.You will still get the Option screen at start up, but will now have your former Linux drive available for XP.
If you presently do not get the option screen at start up. Just reformat the drive with Mandrake installed.
If you are unfamiliar with formating a hard drive, click on help and check out formatting.It contains a very easy explanation of formatting and all the options.
I have two hard drives in my HP, one with XP sp2, and the other drive has Linux Mandrake. How do I remove Linux from the second drive (I'm pretty sure it's the slave) and free up that drive so I can use it for XP? I'm not very computer savvy, so if you can help please don't get too technical on me! Thanks very much.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic