Cannot edit “mail format” in Outlook2000

I rolled out Office 2000 to a remote office of 7 users using the same method as done before, via MSI/CMW files but disconnecting each PC from the network and installing locally (for some reason it kept trying to connect to a remote-based server where the install files – on CD – were originally based). However when users try to edit the “Mail Format” tab in Outlook2k (Tools, Options, Mail Format) everything is greyed out and Word is set as the default email editor and cannot be “unchecked”. Doesanyone know how I can enable this window? I’ve looked at POL files but no joy, I’ve installed Office2k using same procedure on another standalone PC in my office and this problem didn’t occur. All ideas welcome.