I take it you're using some sort of cloning system to image the client computers? If so, the problem is likely that the the relevant preferences are stored in ByHost preference files, meaning that they only apply on one particular computer. The reason for ByHost prefs is so that if you're using a network account and logging into multiple client computers, you can have separate settings for each one. Unfortunately, this also means that when you clone one computer from another, the preferences stored in this format don't stick.
Most Mac imaging systems have an option to rename the ByHost preference files so they do apply to the newly imaged computer. If you're doing the imaging manually, or using a system that doesn't have this option, you'll need to find a script that handles the renaming. Unfortunately, after a little googling I can't seem to find a script to handle this, though I know they exist...