Yea that's it. Just to confirm, you should take a picture and post it up. IF it is a PCI-e slot, and all the minimum requirements match for D3 (I don't know what they are), then you should be able to purchase a video card and go from there.
At this rate though, I would spend $500.00/$600.00 or so to build another system. You already have the monitor and miscellaneous sh*t, so maybe you can just shop for the tower itself.
Seems like you need a newer computer anyway!
