I presume you have got a 9 pin d-sub connector male to male.
All depends on your G-card.
Each have seperate software to enable video modes. It is much easier to use a laptop as they have inbuilt video splitters.
I presume you are connecting to your other monitor via DVI.
Just to test is unplug your current monitor, plug in the VGA lead in to your TV and the other to your PC. before you do this make sure your res is 1024*768.
and see what happens