I've looked high and low for a solution to this with no success and so am
posting my question here. Please forgive me if I've overlooked the solution
somewhere.

We used the Office Customization Tool to configure the default Outlook 2007
message format to Rich Text. We have several users who prefer to use Plain
Text but have encountered problems do so on a global basis for all new
messages. It appears that when Outlook 2007 is installed on Vista, the end
user is prevented from modifying this setting within Outlook (the options are
grayed out). I've tried updating an existing installation with a new MSP
without success and have run out of ideas as to what and where to change
things. I've tried using:

Microsoft Office Outlook 2007\Tools | Options...\Mail Format\Internat
Formatting\Outlook Rich Text options = Enabled (Convert to Plain Text format)

Microsoft Office Outlook 2007\Tools | Options...\Mail Format\Internat
Formatting\Message Format\Set message format = Plain Text

These have no effect on the Outlook settings in the GUI.

I've even resorted to modifying the registry directly but the Outlook
settings remain the same.

Any suggestions as to how to overcome this limitation are greatly
appreciated.

Thanks!