If you have a video card that is using WDDM drivers and supports DirectX 9c but is not allowing you to use vista glass, there is a trick that you can use to force Aero to run. Follow the steps below:
1. Click on the start button and key in regedit and hit Enter.
2. Navigate through, HKEY_CURRENT_USER, Software, Microsoft, Windows and DWM.
3. Set Composition to 1 and CompositionPolicy to 2.
4. Restart the DWM by restarting the Desktop Windows Manager Session Manager service. This can be done in services.msc or by typing
net stop uxsms
net start uxsms
at command prompt.
Aero Glass should be enabled by default if your video card supports it. If it is not enabled, you can turn Aero Glass on using the steps listed below:
1. Right click your desktop and click Personalize.
2. Select Windows Color and Appearance.
3. From the list of color schemes, click Windows Vista Aero.
4. Click OK.
Once the service restarts you will have glass!