Is your CPU working overtime for no apparent reason? Resource Monitor offers the best way I know to find out which program or service is the culprit. The default sort order uses the last column, Average CPU, as measured over the previous 55 seconds. Watch the CPU column to see whether a program is using little spikes of CPU time or is working nonstop.
For a much more detailed discussion of how to use Windows Vista's built-in utilities to find and fix performance problems, see
Fixing Windows Vista, Part 3: Top Troubleshooting Tools.