Sounds like you are running Windows XP or Vista. They will never run fast with only 512 MB RAM. Install Linux and your computer will run like a rocket. Or try a Linux Live (no need to install) and your computer will boot in less than 3 minutes with thousands of programs ready to use.
Try Knoppix, PCLinuxOS or Dyne:Bolic.
This will negate his games, though. Especially the Cabala one that he plays.
I think also you need to free up some hard drive space. Once a hard drive gets to about 90% full, it starts to slow your system down. You could get a hard drive, and some ram, but in all honesty I think you should save fora new PC.
CCleaner is a good place to start, and free up some HD space.