Hell, MS has a program that when your taking computer administration-related classes you can get your OSes for free.
I was taking networking classes so I had at one point: XP, w2k, w2k server, w2k advanced server, and even w2k advanced database(datacenter?) server.
All of them free, normal levels of support and updates as long as I attend classes. Then after I finish classes I can continue using them. Personal use only, of course.
(I still prefer linux though. 😉 )