Buy an Nvidia GeForce card, at least a 660's worth of power with as much video ram as possible.
I'm currently using a 660ti with 3GB video ram (with an Intel i5 3570k), and can run BF4 on Ultra comfortably (40-60FPS all the time, no drops).
I was thinking about a GeForce GTX 770, along with the Radeon 9000 for a great performance. Probably a bit overborad, so I might choose a lower GeForce.
You can't mix brands for dual-card setups. You have to have either two AMDs or two Nvidias, and they have to be from the same chipset family (i.e. two Radeon 9xxx's or two Geforce 6xx's).
You won't get much benefit from having two graphics cards in SLI/Crossfire either in my opinion, it causes more hassle than solution - especially when you are trying to play an older game or any game that does not explicitly support more than one graphics card.
Most games on launch actually perform worse in SLI/Crossfire mode until the developer finally gets around to adding support for it.
So could I buy the same exact AMD Radeon 9000 and expect an improvement? Or do I have to buy a better one?
Can you post a link to the exact card you have? I could give a more accurate answer that way.
Also about to leave for lunch but I'll be back to respond later.
i looked up how to find out what graphics card how have and it turns out that I have an AMD Radeon 7900.
It's custom built.
Before I say anything else I want to make sure that your problem is your GPU and not your CPU.
Pick a game (recommended: BF3/4 or Crysis 2/3) that is very demanding on performance and adjust the settings until you can just barely enter a playable state of the game (i.e. 30+ fps with no drops). Once you are at that point, push the settings a bit higher and start playing. After you get into the gameplay and things start to lag, minimize the game and open task manager - switch to the CPU tab. If the usage graph shows your CPU was running at a constant 90-100% load at any time while you were playing, then your bottleneck is your CPU. If the load did not hit 100% but you were still lagging, then your GPU is the bottleneck because it can't handle the load.
In my case if I play BF4 on ultra my CPU never exceeds about 60-75% load, which means I could get better performance by upgrading my GPU (the CPU could still take 25-40% more load before it became the bottleneck).
So assuming your bottleneck is your GPU, keep reading. If it's your CPU, buy a $350 3.7Ghz i7 4280k and then re-evaluate your performance and bottleneck.
get about 35-60 frames per second (it depends on what's going on in the game).
I don't know what you mean about task manager.
35-60 is a large range and does not result in smooth gameplay. Ideally you don't want to see a variation of over +-10FPS, otherwise it becomes noticeable and has the effect of an FPS drop.
If you open task manager and go to the Performance tab you will see something like this:
Follow my instructions and it should make sense.
I found task manager, and I'll try a test.
You should be able to get at least $210 for that card if you choose to sell it.