In your Ubuntu dash home (icon on the top of the list on left side), search "Desktop sharing". It will show "Desktop sharing" icon, so click on it and it will launch the "Desktop sharing prefereneces" window. Then change preferences and "Allow other to see your desktop". For any more details, just click on the "Help" button at the left bottom the "Desktop sharing prefereneces" window.
Last edited by shivaa; 11-05-2012 at 10:44 AM.