AMD Athlon XP 3200+ is the best that will go in that box.
Since you have an Nforce2, its a much better overclocker you might try overclocking it as long as you've got a decent cooler.
HOWEVER, you might as well buy a new system, thats 8 years old.
Here's a good system. I know some of the other forum members will dis it for being slow compared to an "I7 2600k" or "Xeon X999999999999", but its at least 5 times faster than an XP 3200.