If your university doesn't have MSDNAA - and almost any decent CompSci/IT/etc dept should have it - you can get MSDNAA through IEEE. I don't think there's any program requirement for IEEE other than being a current student. IEEE student membership for one year is $15.
MSDNAA comes with multiple copies of every version of Windows, Visual Studio, and all sorts of other pricey MS software,
Both ACM and IEEE student memberships come with MSDNAA access. The selection they have is larger than I've seen with three different universities' MSDNAA for CS students, although maybe not always that useful.
ACM offers Win 7 Professional (RTM) no more. It was pulled this week after a huge growth spike of people joining and going after several Win 7 licences.
MSDNAA comes with multiple copies of every version of Windows, Visual Studio, and all sorts of other pricey MS software,