You mean like this?

Just drop a PCI-compatible video card in an open slot for each monitor, plug in the monitor, and away you go (that is, assuming that your video card will only drive one monitor; my current set up uses multiple ATI Radeon X1900 XT cards, each of which can drive two 30-inch displays from one card if you want to, although I dedicate one card per monitor for the increased performance).
-dave