Budget upgrade build for gaming

[redhot91gt]

I am currently looking to spend around 350$ to upgrade my current system. If the whole system has to be trashed to get the performance I want, then I will have to live without the upgrade for now.

My current system is quite old.
Here are some specs:
AMD Athlon 64 X2 3800+ 2.0Ghz processor
Biostar Geforce 6100 AM2 Micro ATX MB
2 x 1GB sticks of G.Skill DDR2 800 Memory
Cooler Master RP-500-PCAR 500w power supply
Western Digital Caviar 160GB 7200rpm 3.0gb/s sata drive
XFX Geforce 9800 GT

Its been a long while since I have researched hardware. So I really don't know what is good and bad, or good value.

My biggest question is... What components are holding me back the most? I am looking to play World of Warcraft without fps issues on high settings. I would also love to play some of the current games on low settings, Like Saints Row or maybe even battlefield 3 (though this isn't mandatory)

I know it will probably be hard to get this done under my budget, but I am hoping I can use the Graphics card and hard drive and just replace the MB/CPU/RAM with something better. Though, I really have no Idea what is holding me back the most.

Any help would be much appreciated!

PS: I am not brand loyal on anything really
EDIT: I wanted fill out the template I just found to help the advising.

Approximate Purchase Date: As soon as possible

Budget Range: 350$

System Usage from Most to Least Important: World of Warcraft mostly. Wouldn't mind new games on lowest settings, but not mandatory

Parts Not Required: see above... Requires advice I have a case as well.

Preferred Website(s) for Parts: Newegg is always good, but open to suggestions

Country: United States

Parts Preferences: No preference

Overclocking: No

SLI or Crossfire: No

Monitor Resolution: 1280x1024

 

[Proximon]

You can get a new platform started, and it should help. Yes, it's all slow but you can get on an upgrade path still.

So, you likely need a better cooled case and your PSU is poor. We can just take care of that too. Please note the case is on sale and you need to move fast on it.

■Rosewill Smart One ATX Mid Tower Computer Case, Black interior, comes with three Fans-1x Front Blue LED 120mm Fan, 1x Rear ...
■ASRock 870 Extreme3 R2.0 AM3+ AMD 870 SATA 6Gb/s USB 3.0 ATX AMD Motherboard
■Antec NEO ECO 520C 520W Continuous Power ATX12V v2.3 / EPS12V 80 PLUS Certified Active PFC Power Supply
■PNY Optima 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) Desktop Memory Model MD8192KD3-1333
■AMD Phenom II X4 960T Zosma 3.0GHz Socket AM3 95W Quad-Core Desktop Processor HD96ZTWFGRBOX
TOTAL: $334.95

 

[DoomsWord89]

Indeed, starting a new build would likely be your best option.

 

[redhot91gt]

Thanks for the info. I may just save up for a better video card too. Not sure yet.

 

[DoomsWord89]

I see, what GPU are you thinking about purchasing?

 

[redhot91gt]

I am not quite sure. I have seen some people recommend Radeon HD 6870's, I may go with something like that. Is this a good choice?

 

[Proximon]

Well, possibly even overkill at that monitor resolution, but a good choice.