Create or modify the DWORD registry value:
HKEY_LOCAL_MACHINE\Software\Microsoft\Office\11.0\Outlook\DisablePST
Set the value to 1 to disable .PST files, or 0 (default) to enable them.
Note that .PST files already located in a user”s email profile will still be functional. Therefore, you should manually remove all .PST files from the profile prior to setting this value. This also includes disabling the auto-archiving feature, which takes advantage of .PST files.