What's the best possible upgrade for my current comp?

[leech33s]

Hello everyone, I'm a complete noob in comps and I need some help.
I want to upgrade my current rig so that it would be able to run Crysis Real Life Mod and GTA 4 Photorealistic Mod with highest settings with little to no lag.

I hope the budget for the new parts will be around 500, but feel free to go over the budget just a bit.
I am currently having issues choosing the right parts for my current rig. Please help me out, it would be greatly appreciated.

My comp is:
CPU: AMD Athlon X2 244 Dual-Core CPU w/ HyperTransport Technology
Mobo: Asus M4A87TD EVO AMD 870 Chipset CrossFireX
PSU: 500 watts
GPU: ATI Radeon HD 5670 1Gb

I don't want to switch to Intel, just want to stick with AMD.

What is the most cost-effective upgrade for my current rig? Like I said I really want it to run the previously mentioned games above. Thank you so much for your time. I know it's a pain in the a** choosing parts, last time it took me 2 days .

 

[tlmck]

You will want to update your motherboards BIOS to the latest revision(consult your manual), and then upgrade to the highest end processor the budget will allow from this list. http://www.asus.com/Motherboards/AMD_AM3/M4A87TD_EVO/#CPUS

If that is still not enough, then the graphics card would be next. With that power supply wattage, a 6850 card would be about the best I could recommend. It would still be a significant upgrade.

It would also help to know the name and model number of the PSU just to make sure.

You do not mention ram, but 4gb would be minimum, and 8gb better if you have 64 bit Windows(for the 8gb).

 

[Dark Lord of Tech]

http://www.newegg.com/Product/Product.aspx?Item=N82E16819103849

 

[leech33s]

Okay thank you all for your posting! I have ordered the parts!