There are a lot of OEM, brand new legit cd's, hitting the market now from resellers. They are mostly Dell, with some HP. They come with a key that is not counterfeit.
They are mostly from 2002; so you will have a lot of updating to do. I "purchased" (paid for shipping) an SP2 cd from M$ to make that process less tedious.
Most of them will install on any computer. Just make sure when you purchase that the seller states this. Some of the earlier ones had a bios check that required a proprietary mobo.
I've installed about 75 of these for customers, and they are working just fine; and are completely legit.
Buyer beware though; make sure the sellers state that install will work on any comp.