VNC + VIRTUAL DESKTOP + JAVA ACCESS = WIN?

Ok, heres what I want to do:
I want users to be able to connect to my website and through some sort of client, use a sort of VNC on a "virtual computer" that doesnt actually exist. I'm pretty sure they can do this at Flinders University, so I know its not impossible.

If anyone can tell me how to do this, I shall reward thou with CP.

Create a PHP website which starts a VNC client and connects to some machine. The PHP script takes a screenshot of the VNC client and sends this back to the browser. On the browser you have some JavaScript which checks for mouse and keyboard input, which is via XmlHTTPRequest send to the PHP script. The PHP script sends the input to the VNC client and takes a new screenshot which it sends back to the browser.