If You have a powerful AC, than try overclock the Processor.
But I would prefer You to buy new one, the AMD Phenom II QUAD-CORE is about 100$.
The GPU could be for ex. AMD Radeon HD 6670 1024MB, about 110$.
RAM is really cheap these days, 4GB DDR3 1600 MHz will not cost more than 15-20$
Optionally You can also buy a new CPU cooling for better performance (20$)

Everything would cost You no more than 300$, so spare money and Buy it.
Greets, and Marry Christmas !