Want W7? Don't throw away that dead machine with OEM XP
 

Why? It's worth US$80!

For most people, there will not be a need to buy a full retail version of W7 and hence save a few bucks by getting the upgrade version..

W7 upgrade editions (not anytime upgrade or the qualifying vista upgrade) require ownership of any licensed XP or Vista version, even the OEM one that came with your machine.
This means that as long as you still have the Windows genuine sticker with product key on the back and proof of purchase of the machine, it doesn't matter that it fried long ago, you are entitled to install a fresh W7 on a different machine using the upgrade version.
The fresh install of 7 on a different machine without the qualifying OS on it or a disk handy, will require either a call to MS for activation or some fancy footwork to get it activated, but it's all legit and legal.

Go and read the EULA yourself.

Here's an article that explains the fresh install activation process using the upgrade version.

Interesting, but......
 

...not sure why I'd want to now as XP is finally working flawlessly.