This card is just about twice as powerful as your 7600gt. In other words, it will play most games at high settings and medium resolutions (1650x1080 and under). It does need a 6pin PCI adapter to run it however, and judging from your components your power supply is probably not good enough.
The 3650 doesnt need extra power and your system will run it. Now this should play most games medium to high but I suspect your 7600gt already does this. You will notice a few extra fps but depending on your model of the 7600gt I dont think it'll be a difference to justify $80.
Your third option is to get a new system with pci-express where you can get a 4650 for $50 which would blow away all those cards mentioned here and play any game at high settings (minus crysis of course).
The 7600 is a good card, I wouldnt upgrade it. It sounds like you need a PCI computer. The best card out there for AGP is the HD3850, but its getting close that you need a new system. COD4 your processor is just short of the 3.0 GHZ requirement, which means your system is very close to becoming extinct.
When i say cant effort a new system i mean bying a whole new pc.
but not really.. Im gonna get money back from paying to much taxes so i just want the best and cheapest upgrade of any sort so i can play games that are out today. "cause yeah i can pretty much play em all but for most of em theres some minor lagg that buggs me." So yeah no real budget. just want the best and cheapest.
Btw how come i can play stuff like tomb raider underworld, fear 2, Dead space and so on - without laggs and something like COD:WAW totaly kills my pc exept when playing the zombie bonus- What makes the big difference between those games? Ive noticed that fire takes most to display correct...
k but the thing is cant really efford a new system. What do you think the cheapest way is to get what im searching for?
Start a new system. For $200-$275 you can get yourself a badass mobo, processor and new memory, you can use your old ide hd, case, and maybe your PS in your new system. Right there you have a working system. You can add parts to your new system as kind of a payment plan. You say you cant afford a new system, well you really cant afford to put $100-$150 into an dying system.