np Drakus. I have been building my own computers since the late 90s. :-D

I didn't choose a cheap config that cost a little but will barely run MW2 at low resolutions. I didn't choose the latest generation of CPUs and video cards that will cost you over $900 either. I chose something in the middle.

I put the parts you will need to upgrade in a cart on NewEgg. It will be a minimum of $583 (no tax or shipping included) http://i47.tinypic.com/2rptqvo.png
NOTE: I am not sure about the case you have and if it will fit a standard motherboard of if you will have to also buy a new case. A case was not included in the config for $583.

I configured you a computer on the HP website. It will be $539 for the PC and $95.99 for the video card I chose for you from NewEgg ($634.99, no tax or shipping included). Here is a link to the HP cart http://bit.ly/HP-p6250t-010310

You save about $52 if you build the computer on your own. The $52 will give you a warranty for all the parts from a single company, HP and also save you any hassle of building your own computer.