Windows Vista has some great additions. One of them is the new and re-designed Performance Monitor. You can open the Performance snap-in from the Computer Management tool (see below), or as a separate snap-in.
Inside the Performance tool you will find a Monitoring Tools folder, and in it you will find the Reliability Monitor. The Reliability Monitor is a snap-in for Microsoft Management Console (MMC) that provides a system stability overview and details about events that impact reliability. It calculates the Stability Index shown in the System Stability Chart over the lifetime of the system.
Microsoft, Windows Vista, Reliability Monitor, Tips, Knowledgebase