How does the computer determine if it can run Aero?
The Windows System Assessment Tool (WinSAT) queries the system hardware and assesses the hardware capabilities of the computer. The Desktop Window Manager uses the data that WinSAT gathers to determine if the machine is capable of displaying the Aero Glass interface. WinSAT runs once during the Out of Box Experience (OOBE) setup phase but can also be run manually by running WinSAT.exe from the command line or from the Performance Rating and Tools user interface.
For information on manually running WinSAT, refer to the FAQ How do I rerun WinSAT?
Note: This information provided by Microsoft.