[Windows Vista] How to diagnose performance problems in Windows Vista?

This can be done with Performance Information and Tools in Control Panel. Performance Information and Tools can be used to check problems of many programs and revising them automatically.
1. Click the Start button, and click Control Panel.

2. Click System and Maintenance.

3. Click Performance Information and Tools.

4. Displaying Performance Information and Tools screen.
Click the items appearing in Rate and improve your computer's performance.
5. Different details will appear according to different items. Click Help to show how to avoid the problems.

*Performance diagnosis provides two ways to check and maintain Windows Vista general problems, such as media cannot play normally, applications start slowly, operating system starts slowly, and the network connects slowly etc.
Once the performance issues are confirmed, please see this FAQ - [Windows Vista]How to evaluate the PC's performance.