I am not sure if you are aware but MS does not support PST files that are accessed over a network. This is because they can become corrupted. PST files should be stored on the local machine and then backed up to a server.
If there are PST files have become corrupted then you can run SCANPST.exe. You will find this program on your local machine, if you do a search for it. TIP: Copy the PST file to a local machine, and then run SCANPST from there, if you try and scan a PST file that is on a network drive, it will take a very very long time and sometimes fail.
Also be aware that if PST files become to large that can also cause problems and lead to corruption. Make sure that your users are creating the correct PST files. There are two options within in Outlook 2003. One of the options will allow slightly larger storage.
Sometimes it maybe an idea to get the user to create another PST file on there local machine and move the email from the old PST file to the new one.