Need Good Computer Build

Hello I am looking into building a gaming PC with the best bang for the buck. I myself am not sure which chipset is better AMD or Intel. I game on MMO and FPS and like to learn HTML,CSS and things like that. I want a motherboard and chipset that will best perform with the graphics card its designed for.

Other than playing games on my PC I do script and fool around with stuff but I want to focus simply on the gaming aspects as everything else I could go without.

My Price range is 300-500$, Its not alot but I also want to point out that I only need a internal hardware, I have an X-Blade case which is large and can fit almost any Motherboard and Graphics card. I can get Hard Drives and DvD/CD Drives myself.

So pretty much I am looking for
-MotherBoard
-Proccesor
-Graphics Card
-RAM

I can get the power supply and all other parts.

My current build is a
P4 3Ghz Processor
Intel Genuine motherboard
1 GB RAM
Nvidia 512MB 6200LE

Anything better with a good price I would appreciate alot

Thank you and I hope I provided enough information(AMD or Intel is up to you)