Is it possible to run two windows sessions from the same computer at the same time?

Interesting question. Well there seems to be 2 hurdles, the bigger of the two would be multiple instances of Windows. To overcome that challenge you could use Virtual Machines. Use a single host and create 2 virtual machines and just drag each VM on a screen.

To overcome your problem with input devices I found an article on a tool someone found who was trying to do something similar. It looks like it handles multiple input devices. You would have to install it on the two VM's and hopefully be able to isolate one set of devices so that each VM has it's dedicated keyboard and mouse.

Here's the link to that article:

How To Use Multiple Keyboards and Mice On One Computer

In two words : you can't.

This artificial limitation by Microsoft is designed to force you to update to a Server version of the operating system.

However, see this:
Enable Concurrent Sessions on Windows 7, Windows Vista and Windows XP (Termsrv.dll)

So long as you understand that actually executing these instructions is a violation of the Windows EULA.

This is possible with Windows Multi-Point Server. It is not for retail sale, and is only available to educational departments.

For a demo, see YouTube.