Just read this on Lifehacker:
Not every university has a deal with Microsoft to provide cheap product licenses to students, and high schools are generally on their own. There is, however, a way for any math, science, or tech-inclined student to score some slick deals.
The CyberNet blog points any student with an interest or inclination toward the "science, technology, engineering, and mathematics fields" to check out the Association for Computing Machinery (ACM), where a membership is $19 and one of membership's key perks is access to Microsoft's MSDN Academic Alliance catalog. That lets you snag Office and other normally high-priced products for very low prices, and Windows 7 Professional licenses for free, minus the cost of membership. A single validation key for Windows 7 Professional at the cost of a pizza is pretty good, but CyberNet sweetens the deal by noting that picking up eight separate keys for 32- and 64-bit version of Windows 7 in four different languages gives you eight keys that work on any installation. That's a seriously cheap family upgrade pack.
The catch, of course, is that the ACM has to approve your membership, and that requires being a high school or college student with some kind of provable interest in the math, science, or tech fields. If you happen to be that, though, there are eight license keys with your name on them, each costing less than a tall latte.
Open to UK students too.
WINDOWS 7 is not available through msdn acm any longer!!!!