I would start by 2 things... Buying a new case, swapping all the parts over to it.
The other thing, and I forgot about this, What size of power supply do you have? A 470 needs some good power of atleast 500W...
That, if not upgraded, could easily also slow you down, though I'd think you'd BSOD too.
So, I'd start with a new case and quality psu, in abouts 600W so that youre good for a few more upgrades in time.
The biggest thing thats hurting you is the oem prebuilt. They lock the bios, so you can't over clock and they limit the cpu's you can upgrade too.
Hmm, I can not find anything on your system, Do you know if the memory is DDR2 or DDR3?