One missing feature of the task manager in Windows 2000 and XP is the option to momentarily freeze a process. Setting the priority of the process to idle will not give the desired result.
For example, if you're running a process that consumes all the CPU time available, this causes the CPU to run at 100% capacity all the time. Even if this process runs with idle priority, it will use the CPU when possible. To prevent over-heating of your pc or laptop, you can freeze these processes when you're away from your computer.
The windows of a frozen process will remain visible, but will not be re-painted when another windows moves over it. Note that mouse-clicks and keystrokes are still sent to the process and will be executed as soon as the process resumes.
Warning: pausing and resuming processes might be harmful to your system, so use it with caution. To prevent serious damage, pausing of system processes is disabled.