http://dmc4.orcon.net.nz/1.jpg
Assuming ( :d ) that you have a geforce, make sure you have 'clone' enabled and that when your not playing a video the picture on your tv is that you see on your main moniter.
http://dmc4.orcon.net.nz/2.jpg
Then change that box to 'secondary' and it should play videos on the second moniter in full screen while just being a normal window on your moniter. This should work for most media players and works especially well in bsplayer :)