This is EASY...
1) Select “Remote Desktop” from your preferences menu.
2) Now activate the check box “Allow other users to view your desktop”.
That’s all! You can now vnc to gnome* from your windows box using the
vncviewer application on port 5900 (unless you change the default).
*Note: You must be logged in to Gnome for the server to be running. If you want to be able to login via VNC to GDM/KDM then this is a bit trickier and I will only cover these steps if they are needed because its a pain in the arse.