Windows Server 2008 for free

You can get Windows Server 2008 evaluation for 240 days for free - see http://trycatch.be/blogs/roggenk/archive/2008/03/02/windows-server-2008-trials.aspx (you have to re-arm (shouldn't that be "re-disarm?") the activation period each 60 days, but I'm sure Windows will remind you :)

That's about eight months for free. You can always zap your partition and reinstall again when it expires.