From a thread I’ve took part in, there are currently no settings in the official office 2003/2007 ADM packs to control this setting.
Here’s the registry how to:
For Outlook 2003:
1, Click Start, click Run, type regedit, and then click OK.
2, Locate and then click the following registry subkey:
3, On the Edit menu, point to New, and then click DWORD Value.
4, Type DisableEditPermissions, and then press ENTER.
5, Right-click DisableEditPermissions, and then click Modify.
6, In the Value data box, type 1, and then click OK.
7, Exit Registry Editor.
For Outlook 2007, that is HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Options\Folders