Where's the Windows Vista Aero Theme?

Great question and here is the answer.

If any of the following statements is true, you will not be able to run the Aero (glass windows) theme:

•The copy of Windows Vista is not a validated genuine copy.
•The video card does not support the Windows Vista Aero theme.
•The video card supports the Windows Vista Aero theme. However, the video card is configured incorrectly. For example, the video card may be configured to use only 32 megabytes (MB) of VRAM.
•There are no Windows Display Driver Model (WDDM) drivers available for the video card. If the computer has more than one video card, this issue may occur if only one of the video cards does not have WDDM drivers.
•The computer has more than one video card. However, the video cards are not from the same manufacturer.
•The version of Windows Vista that you are using does not support the Windows Vista Aero theme.

To find out which of these problems is preventing you from running Aero (and see if anything else will be affected or prevented by upgrading your PC to Vista) download and run the Windows Vista Upgrade Advisor.