The intel Pentium has 2 cores,3.2Ghz (Not really sure is higher or lower is better in Ghz, I'm still kinda new to this), and a 3mb cache.
My current processor has 4 cores, 3.6Ghz, and a 4 mb cache.
GHz/Cores/Cache =/= Performance.
Still, I wouldn't bother with a CPU upgrade. The difference between your current processor and the Pentium is not worth $100.
What power supply do you have? Knowing would help with suggesting a graphics card.