The Processes tab in Task Manager (Ctrl Alt Esc) provides a reasonable amount of information. You can get a wealth of useful details, including the Process Identifier (PID), by clicking View, Select Columns, to open the dialog box shown here. To see all running processes, including those under the system's control, click the button in the lower left corner.
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.