May I suggest you grab more RAM. Try upping to 2 GB, even. XP can't really handle any more, so it shouldn't be too expensive.
How big is the memory on your Video card? Is it an integrated system? If so, after you get the RAM, try upping the memory your system can use for Video, and see what happens.
That, and see if your Drivers are up to date on the Video card/chipset. Might smooth things out a bit, even on an older system ;)
Just my 2¢ on it.