The Windows NT Performance monitor has an ability to monitor the CPU usage, and if needed you can set Alerts which can trigger events such as writing to the NT Event logs, running a DOS application or whaever else you can think of.

Performance monitor is available in NT4.0 and 2K [and XP].

The Alerts are specified under the Performance monitor program.

You normally have to be running the Performance monitoring program in order to get alerts, but you can monitor multiple counters at once - which may be more useful than a strict CPU usage utility.

Hope this helps.