Agreed. You're card was a mediocre card 3 generations ago. Although it will "play" most games, you will not have a great experience while doing it. Assuming that is the PCI-E version, you should probably look at upgrading it...possibly HD5770 or the nvidia 460. You're gaming experience will increase 10 fold ;-)
Yeah dude, my last PC before i got this one had the Core 2 Duo, 6gig ram and an 8800GTS, and that still managed to play modern warfare 2 at max, just had to turn off anti aliasing. Did crysis at medium quite easily too.
You will find that these days frames are limited to the power of your graphics card. So find a card that fits within your price range and your power supplies ability and you will see a massive performance gain.
For better gaming performance? No that was not a wise decision, you should have spent a lot less on the CPU and bought a decent graphics card like a GTX 460. The 9600GT is stronger than your 8400GS but only good for lower settings and resolution gaming.
I give 8400gs 1 out of 10 for gaming , actually 7300Gt us better , GS series is very bad for gaming , I recommend you 4670 or 9600 Gt as agaming card and very cheap if you 're able to buy them as used .
crysis will eat ur video card and processor for breakfast.if ur on 1680 1050 resolution a gtx 260 or a 5770 will play it fine.at 1920 1080 u need a gtx 460 if ur on 1280 1024 u need a 8800gtx or a gts 250 to max the game