I looked around and figured out your motherboard is this:http://h10025.www1.hp.com/ewfrf/wc/document?lc=en&dlc=en&cc=us&docname=c00361570
The specs list zero PCI-Express and AGP expansion slots. There are a few PCI graphics cards out there but I think the larger hardware issue is your entire computer. It's pretty outdated and I would consider an upgrade. You can always stick with XP Pro, which is still largely more stable than Windows 7.