There have been quite a bit of news recently about the Windows Vista upgrade DVD not really needing anything to upgrade from. You can do a clean install of Vista without putting in the product key, and then upgrade that installation. That talk has led to some talk about doing a clean install of XP, which led me to the website of Michael Stevens. He is a Microsoft MVP and has a good article about doing a clean install of Windows XP. The article is very through and has links to other resources that you might find helpful.