on one graphics card, the vga, dvi and hdmi ports run at the same lane and you can only use 2 monitors on that lane, however ati's 5xxx series have added a display port which runs on a different lane resulting that you can use more monitors, nvidia have added so that if you run 2 of their new 4xx series in sli you can use up to 3 monitors. but your graphics card is a built in one, so you can't run more than 2 if you have 2 ports (either vga,dvi or hdmi)