Regarding your cooling problem, get a software sensor to test your temperatures, use something like Motherboard Monitor 5.
Now for your cpu, since you don't want to get a new board or a new comp, then you'll have to get a better XP processor. When you say you can't use XP 3200+, how do you know that? I would assume your socket supports up to 3200+, which is the fastest XP processor out.
Whatever you do, be sure to solve that cooling problem first.