It could very well be that the AMDK6 is a bit too slow for DivX. An AMD K7 is recommended... You could try reinstalling the DivX codec but I think it won't help you'll just have to ask your boss for a new computer
Some tips to help you with playback:
-Lower the screen resolution to 640*480 for instance.
-Shut down all other programs running in the back.
-Do NOT use MediaPlayer (heavy CPU usage).
Goodluck