You can not do that with Windows 7 or any desktop version of windows without replacing DLL's (This hack only works if you do not have SP1 installed, so you are leaving your self open to virus attacks that Microsoft has patched for, I do not recommend this approach).
If you want to support multiple users at the same time using the correct methods you will need to buy Windows Server 2008 R2 (the server version of Windows 7) or newer.