What you need to do is the following. Your card doesn't support nview/twinview so it can't display to two screens at a time. (possible using a trick at only 50/60 Hz ...).
You need to use two XF86Config-4 files (or one file containing multiple serverlayouts). Then start a second Xserver using the second XF86Config-4.tv file: startx -- -xf86config XF86Config-4.tv :1
Then switch between both servers using ctrl-alf-f7 and ctrl-alt-f8.