someone give me an old PC. I would like to install driver for the graphics card, but I don't which brand it is. How can I know which card is inside the PC?

Assuming it's Windows, go Start->Run->dxdiag then once it loads (may take a bit), go to the Display tab. It'll tell you all about your card there.

Easier is to right-click on the desktop and select Properties. Click the Settings tab, and it should say "<Your monitor type> on <Your graphics card type>" in the pop-up menu in the middle.