It is setup like a trial edition of Windows. It can be installed on anything really. Microsoft say the requirements are Windows XP and Above, but i did see code to convert from a VHD to a Virtual Box image. Also, you only need to download every 3 months if you want the latest, patched edition from MS. If you want to do it yourself, you can just recreate the image yourself (sysprep).
The 3 month expiry is what led to my company paying for licenses. Having to potentially pause development and spend time doing the same setup process 4 times a year is painful (and wasteful since there's no real reason apart from trivial licensing issues - the resulting install is the same).
