We have these PCs in our IT lab in school, that was built at least 6 years ago (I've been here 6 years and they were there when I joined). They are terrible at even normal everyday tasks, I wouldn't expect much from them in any game TBH
(Now the CAD lab is another story, 30x XPS 640's
)
All you can do is turn everything down to the lowest (don't worry about AA/AF, I don't think the onboards chip in them supports it), and play in 800x600. It won't be pretty, and you won't have massive frame rates. But it should be playable then
There isn't really anything else you can do apart from add more RAM, which should help a bit (onboards GFX + low RAM = fail). Changing the CPU might be an option if you found a cheap replacement. P4s are good for 3.0Ghz-ish on those sockets I think, so it's an option at least