Have you checked the following:
Outlook 2003 includes a new setting -- turned off by default -- to allow forms in shared mailboxes to run script.
You can change the setting by choosing Tools | Options | Other | Advanced Options and checking the box
for Allow script in shared folders. You'll see that there is also an option for Allow script in public folders.
Enable both of these.
(The corresponding registry values are in the
HKCU\Software\Microsoft\Office\11.0\Outlook\Security key -- SharedFolderScript and PublicFolderScript, both DWORD values.)
Note that these settings affect both script in custom forms for items in public folders and script in folder
home pages for such folders.