Yeah, wrong section, but hey, you still deserve a warm welcome.
Anyway, this would probably be your best bet if you want something along the lines of 3 GHz: http://www.newegg.com/Product/Produc...82E16819116027
80 bucks, but the 478 socket CPUs have been discontinued, I think, so thats a pretty good price.
Heres a good list of processors that fit the 478: http://www.newegg.com/Product/Produc...nd&Order=PRICE
Also, I'm sure you have heard from computer enthusiasts, whatever you do, don't get a Celeron. They have a very small or even no L2 cache, meaning they are a hell of a lot slower than most processors.
I have to say this, but if you can afford it, I would just get another rig. That is a little outdated to current standards. I saved that for last because I realize this is not an option for some.