In Australia, most retailers will sell OEM software with ANY of the following components: mobo, CPU, hard drive. You don't have to buy all of them; just one of them will suffice. Not sure how this fits with M$ EULA, but nearly all retailers do it here, so it can't be too bad.
Maybe check with your local M$ agent to get it crystal clear? Anonymously, of course!

Cheers
Mick
edit: CPU, not RAM

Ya put me off, lost!