Sounds pretty impossible but TheRasteri has made a video out of it to test out how smooth or bumby is the upgrade process of Windows. He used VMWare and also tested out some games like Doom 2 and Monkey Isalnd.
If nothing else this video will give you the walk through of how Windows GUI or the user interface changed over time. A must watch if you love to use windows.
The only version of Windows that was not tested was Windows ME as it cannot be upgraded to Windows 2000. If you cannot see the video above, here is the direct link. Via WinRumors
