Windows XP
Right click on your desktop and select Properties from the contextual menu. This will open the Display Properties window.
Click on the Settings tab at the top of the Display Properties window and then click on the Advanced button. This will open a new window. Click on the Adapter tab to display information on the video card you have installed in your computer.
Windows Vista
Right click on your desktop and select Personalize. Choose Display Settings. The Display Settings window will show you your graphics card as indicated below by the red arrow. In this example the graphics card is a Radeon X550.