This is for those who work usually on systems through VNC, I am one among them. It was very cumbersome for me to select tabs in the VNC system using mouse and not able to use ALT-TAB functionality. Hence when I searched in Google for any solution, I found a very simple soultion.
Just change the ALT-TAB key binding in your linux machine to something comfortable for you. After you have done this, whenever you select ALT-TAB, the system passes that key-binding to the VNC window.
The solution is just that simple. :). Enjoy.