Run dual monitor AND output to TV at same time?

I would like to run dual monitor (extended desktop) and output to TV at same time. I am using a Radeon 4870 on a Gigabyte P35 QD6 but I have to disable one monitor in order to have TV output via the S-Video.

Would putting another GPU in the other PCI-E 16x slot allow me to do this?

yes it would. To my knowledge most cards will only allow 2 displays at one time. There might be some higher quality cards that let you do that but i am not sure. Having 2 cards would allow for 4 displays.