Windows doesn't understand multiple logon sessions (except perhaps XP & terminal server). VNC server for windows serves the current desktop, not a unique session. The Unices can serve multiple independent sessions, with different shells etc... The VNC site is really the best place to look for details, it's got really good documentation.

I've never tried the true VGA driver, but the less info you've got on screen the better/faster the refresh rate will be. The VNC client (at least the Windows one) has some really handy features, like a 'Send Ctrl+Alt+Del' command for unlocking/rebooting/task managing a Win box.

-Zeke