We had just installed some extra RAM onto a Terminal Server running Microsoft Windows Server 2003 x86 (32-bit). We had also enabled Physical Address Extension with the /PAE boot.ini switch.
Following these changes Microsoft Office Outlook 2003 failed to start. Each time we loaded Outlook, it would crash complaining of a failure in outlook.exe, module mspst32.dll
We fixed this issue by installing Office 2003 Service Pack 3 (SP3).
According to this Microsoft KB article adding the /PAE switch was to blame.