Sounds more like video card than MB. Most of the gforce mx 4 series were AGP cards. Some had fans that failed, many just had heat sinks. I have two still in running systems.
Yours is an integrated onboard in an ASUS mfg (to hp specs) mainboard using the nforce chipset. (mpeg2 encoding is done via the chipset)http://h10025.www1.hp.com/ewfrf/wc/documen...076&lang=en
I suspect the drivers you download from HP are tweaked for the video and chipset more than the current gforce reference drivers from nvidia.
Did you do a recovery install of the xp home from the recovery dvd set or use the recovery partition?
If you used a different xp version or a retail xp home, you might need to locate hp updated drivers (video AND chipset) and test them.
The screen artifacts you describe are usually caused by failing memory when it is on cards, but yours is onboard and uses your system memory.
Your system also should have an open agp8x slot but no pci-e slots. So a replacement video card should be agp8x or standard pci to work.