I'm...not that smart with computers, but here's my problem.

I just got a new computer about a month or two ago, and tried playing Gunz the Duel with it. For some reason, after leaving the game on for about 10 minutes, it starts acting up and my character might start running into invisible walls, rumbling a lot, and all these other weird things. Someone said it might be my graphics card, so basically I just need to know what kind of card I should get to stop the problem, how to check what card I have now so I know what not to get, and I need to figure out how to check my computer's system specs. So, can anyone help me out here?

(Like I said, I'm not that smart with computers)

Oh, and this is a Gateway computer, and I already tried getting an NVIDIA card, which is what was on my old computer, but it isn't compatible.

Edit: Want a free card, if possible.

First of all to check what kind of card you've double click My Computer, in the upper lefthand side there will be a tab called system tasks, click on View system information. Once you hit that go to the tab HARDWARE.Once you're there go to device manager, click on display adapter and it should tell you what type of card you've. You might have to research you Motherboard to see what type of card is compatiable with it and your chipset. (I don't think your going to get a free card to many places)
Hope this helps.