Despite the specs of those machine they got a lot of potential for cheap but stable retro builds however check out the power supply! I have had several of those machines over the years and the most common problem is the power supplies overheating and frying. Seen one where even the board was bricked from the failed psu.

My sister still has her old HP Pavilion (P3 700) and the case looks almost identical. nforce4max is right though, keep an eye on the power supply; her HP wouldn't power up about 4 years ago, and on a hunch I disconnected the PSU and temporarily hooked up a spare I had. It came back to life just fine. Found a suitable replacement, and no more problems. Her children now use it to do homework and play old educational games.

My first computer was one of those, albeit a bit newer, had a 1.1ghz Celeron, was eventually upgraded to 512MB RAM and a Geforce 4 (pci).