When you first install and run Windows Vista, it will calculate your Windows Experience Index score to evaluate your computer's speed and graphics capabilities. Microsoft defines the Windows Experience Index as the following:
"The Windows Experience Index is a new feature built into Windows Vista that is designed to help you better understand how well Windows Vista and other software will perform on your PC.
Your computer, running Windows Vista, is assigned a rating number called a "base score" that is achieved by measuring the capability of your computer's hardware configuration. This base score rating will help you to more confidently buy additional hardware, programs, and software that are matched to your computer's base score."
WEI has been a point of contention for many Windows Vista users because the WEI scores tend to be extremely low. Unfortunately, some software requires your WEI score to be above a certain threshold for all the features to work. Fortunately, it is easy to artificially raise your WEI score by modifying the configuration file.