Auto 'lock Computer'

[Ray]

Hi,
we have a network of approx 200 PC's most now on
Windows 2k or XP some of these we want to
automatically 'lock computer' after a defined period.

This seems to be a standard setup on some new machines,
but not others. How can this be set locally on the PC
without having to go to group policy?

I have seen some suggestions to go to Regedit, but the
local path seems to be different than those suggested.

Any help would be much appreciated.

Regards,
Ray