I'm going to suspect the video adapter driver. I assume you've downloaded the most current Windows 2000 driver? Is this a full system (Dell/Compaq/HP/IBM/Gateway/etc.) or is it assembled from parts? When the video locks, is the machine still operational? Can you make network connection to it? Or is the entire system frozen? You might try swapping out the video adapter with one of a different make/model and see if that solves the problem. I had a similar problem with a Dell system using an ATI Radeon display adapter. I was not able to correct the problem using drivers either from Dell or from ATI. To be honest, the lockups did not disappear until I upgraded to XP.
This was first published in September 2001