Hi .. How To Check My Graphic card specification from Mac Leopard 10.5 and how to change the setting related to it performance ..

Your hardware specifications will show up in system profiler.
Go to the Apple menu at the top far left and click on About This Mac.
When the little window opens, click on more info.

System Profiler will open and give you a bevy of information.

I'll let some one with the know-how tell you if you can change the settings of the graphics card and how.