I've written an image processing script in php which is run as a cron scheduled task (in OSX). To avoid overloading the system, the script checks the system load (using 'uptime') and only runs when load is below a predefined threshold.
I've now ported this over to Windows (2003 Server) and am looking for a similar command line function to report system load as an integer or float.
You can try this at a windows command line. This works in XP, get a lot of other info too.
wmic CPU