If you want to completely disable the ability to create a .pst file through the Outlook user interface, you can use this registry entry:
Key: HKEY_LOCAL_MACHINE\Software\Microsoft\Office\11.0\Outlook
Value name: DisablePST
Value type: REG_DWORD
Values: 1=disable .pst use; 0=allow .pst use (default)
Outlook 2000 would be Office\9.0. There is also a recent Outlook 2003 hotfix that allows it to be deployed in HKCU rather than HKLM, and another one to allow the continued use of SharePoint proxy .pst files.
When DisablePST is set to 1, users will not be able to create Personal Folders .pst files and most features that depend on .pst files will be disabled.
Oddly enough, setting DisablePST to 1 does not disable the ability to open an existing .pst file. To block that feature, you can disable the File | Open | Outlook Data File command with a Group Policy Object using the setting "Disable command bar buttons and menu item." That command's ID is 5576.
See these MSKB artcles:
http://support.microsoft.com/?kbid=258277 (Outlook 2000)
http://support.microsoft.com/?kbid=323244 (Outlook 2002)
http://support.microsoft.com/?kbid=896515 (Outlook 2003)
http://support.microsoft.com/?kbid=897658 (Outlook 2003)
--
Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers