Upgrades for an old computer

[grisvok]

Currently I have a computer that is around 3 years old. I'm looking at upgrading it in some fashion to play video games better. Here is a list of my budget and the computers current specs.

Asus Crosshair Mobo
2 x Nvidia GeForce 7950 GT (SLI)
AMD Athlon 64 X2 Dual Core 6000+ (3.0 Ghz) Processor
850 Watt power supply
4gb DDR2 Corsair RAM
7200 rpm 500gb WD hard drive
Running Windows 7 32bit

Here are my questions:
1) What upgrades can I do for around 400-500$ to make this thing run faster?
2) Does it make sense to upgrade this or will the older hardware create bottlenecking problems for any upgrades?
3) Would dual Nvidia 460's be a sufficient upgrade to make a difference?

If I left out any information i'm sorry in advance. Also, if someone thinks of a few upgrades over 500 that make sense let me know. I'm just trying to realistic with how much I spend on upgrades, at some dollar amount it will make more sense for me to just build a new computer.

 

[calguyhunk]

Seeing as your other specs are pretty alright, these are what you should be looking at.

CPU : AMD Phenom II X4 955 --- $160

Mobo : ASUS M4A89GTD PRO --- $150

GPU : Radeon HD 5850 --- $ 295

You can go with the Radeon HD 5770 for $170 (to stay within budget) and keep the Phenom.

Or if you wanna keep the card which you should, seeing as your primary requirement is gaming, switch to the Athlon II X3 440 --- $77.

You can keep the rest. Oh & btw, switch to Windows 7 64 bit.

EDIT : "Dual Nvidia 460's" are gonna cost you 400 just like that (that's if you're talking 'bout the 768 MB version. A couple of Fermis will set u back by almost 500 right there). What 'bout the rest? You can't really go 'round with an Athlon 64, even after a 500 dollar upgrade now, can ya? And you don't really have a proper upgrade on AM2 anyways.