HP lists no graphics drivers for that model:
http://h10025.www1.hp.com/ewfrf/wc/s...=83505&lang=en
If you have an AGP card it is either ATI or nVidia based.
Unless you want to open the computer and verify which card you have you can try to load the latest drivers from ATI and nVidia. If your hardware does not match the driver it will tell you so.
The other issue here is you have an older card (if you have a card) as that motherboard only supports AGP 4x. This means the newer drivers may not work. In this case you will need to open the computer and ID your card.
Anyway you can try to load one or the other of these:
ATI:
http://ati.de/support/driver.html
nVidia:
http://www.nvidia.com/content/drivers/drivers.asp