Which graphic card upgrades can I get and how to know they will fit?

[TGPROSPECT]

I have a iMac 20" 2.66ghz let me put the spec below but before that.
I want to know what graphics card upgrade i should get or should i just get more ram.

i want to get a 4gb ram package for around $100 so i want to compare which will give better performance in WoW. RAM or Graphics card.
(please tell me what graphics card will work..)

Hardware Overview:

Model Name: iMac
Model Identifier: iMac9,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.66 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 6 MB
Memory: 2 GB
Bus Speed: 1.07 GHz

my current card
NVIDIA GeForce 9400:

Chipset Model: NVIDIA GeForce 9400
Type: GPU
Bus: PCI
VRAM (Total): 256 MB
Vendor: NVIDIA (0x10de)
Device ID: 0x0867
Revision ID: 0x00b1
ROM Revision: 3379

my current ram

BANK 0/DIMM0:

Size: 1 GB
Type: DDR3
Speed: 1067 MHz
Status: OK
Manufacturer: 0x80AD
Part Number: 0x484D54313132533641465236432D47372020
Serial Number: 0x26903D38

BANK 1/DIMM0:

Size: 1 GB
Type: DDR3
Speed: 1067 MHz
Status: OK
Manufacturer: 0x80AD
Part Number: 0x484D54313132533641465236432D47372020
Serial Number: 0x26903DA0



if theres anything else you need please let me know cause im clueless on this kind of stuff.

 

[Hellhammer]

You can't update the video card as it's integrated into to logic board.

 

[TGPROSPECT]

oh silly me

 

[opeter]

iMacs and Mac minis are dead end, in the manner of upgrading. You can upgrade only the RAM and HDD (if not already).