Just a bit more...
I'll guess that your mom's computer uses PC100 SDRAM RAM sticks, and that there are enough of them around in old machines to scrounge that you could get more of them and boost the system's performance.
While you were at it, see if you fall over a quicker Duron or Athlon CPU. Look at the motherboard model and google to see if it has a 200MHz or 266MHz FSB. What the others can't use can be useful indeed. All you'll need is a little thermal paste.
They all look alike, but if you can, read the small print on the face of chip itself.