(Sorry if this is a bit off topic.) The cheapest legal way around the MS OS tax is to join their partner program which is pretty easy to do. It's $299 (annual price) for a 10 machine site license for all of their products (10 XP's, 10 Vistas, etc). Even if you don't renew you still get service packs, etc. If you join the program, you get a nice stack of DVD's every quarter of all of the products with updates. This is much better then $149 to $249 a copy for the normal copies.

They're targeting small businesses with the program but it's pretty easy to qualify if you're a developer or you're trying to run a small business which deals with their technology. This can be helpful come tax time too if you use your setup for business too.