Some one can correct me if I am wrong but I believe with Windows Server 2008 R2 + Windows 7 you can accomplish this.
In a domain environment two users should be able to use the same computer while loading two different environments. You would have your domain account with access to your local files on the pc/network, and when you log out and the other logs in (or fast user switching) they are loading an OS from a VHD (virtual hard disk) off of the server.
All this would be configured through ADUC and HYPER-V. I havent done any tinkering with this as of yet, but I think I have seen the option. It is something that I could try at home in my spare time.
EDIT: Screenshot of the option server side from ADUC...Edited by Deeeebs - 5/1/12 at 9:22am