Wanted: MacOSX with multiple users for VNC...

Right now MacOSX supports multiple users, and all of them can be active. So you can run a long calculation in the background, while the active user runs a different job. Even sound can run in the background. Unfortunately there is no video for a background user, as for instance on Win XP. Wouldn't it be great to have a few background users and each of them having a running VNC server that serves a VNC connection to some tablets or PDAs?