setting up dual monitors is fairly easy...
if you are using a single output agp video card, adding a second video card (and installing the driver) is all you need. if your agp card supports dual output then all you need to do is connect the 2nd display and enable it under Display properties.
if you're currently using onboard video and have an agp slot, simply buy a dualhead card. if it's an an older motherboard, you may have to manually set the primary video device in your BIOS to point to the video card esp if you don't have agp video on the machine.