You need to know what expansion slots the motherboard has available for inserting a video card.
(Click on Motherboard Specifications)
You have 3 PCI slots, one AGP8X slot, and no PCI Express slots. Your best option is to get an AGP 8X video card.
Make sure your PSU can handle the video card you intend to purchase. If it doesn't, you will have to upgrade the PSU.
I've decided to wait on buying a new desk top (PC) for awhile. Decided to upgrade my graphics card (NVIDIA GeForce FX 5600) from my HP Pavilion a450y, XP. Problem - I see there are PCI, PCI 64, PCI Express, etc. The device manager says the current display adapter is found in the PCI bus. What do I need to know to buy the correct graphics card?