if your VGA port is blue it's vga and doesn't support multi monitors
If the port is white, it's DVI and does support multi monitors with the correct adapters.
If your machine is the dell optiplex then it has a bespoke part that will allow it provided you have the ATI graphics option (if i've read it all correctly) but you have the intel option and so it wont work.
A dual head video card will set you back about $40ish.
