Install on another computer, and when you go to activate, it should allow you to install on 2 or 3 different computer configs before it makes you call in the activation. When you call in, they ask you if it's installed on another computer. Make sure it's turned off, just in case, but tell them no. They have no way of verifying, and there's nothing they can do about it. They'll ask you why you're reinstalling, and you tell them you're changing computers or whatever you want.
I know this isn't according to MS's plan, but fuck 'em. You paid for the software, you can use it how you want. I had to do this yesterday. Of course, I have two copies of XP, so I don't need to do multiple installs. But if I didn't have another copy, I would just install it on both of my home computers. MS can suck my nuts. Fuckers are making money hand over fist, and this cheapass activation scheme is just another way to bust our balls. Besides which, even for people using the software legitimately, like me, have to put up with the annoying hassle of calling into a service rep everytime we reinstall. Everytime I use my copy of XP Pro from now on, I will have to call up that fucking number. It's a minor inconvenience, but it's an inconvenience none the less. I shouldn't have to tolerate this bs. Once again, MS can kiss my ass. PEACE.