OntarioMedicalAssociatin,
I am not aware of any such setting in Outlook 2007 natively. However, you may find an Expert here who can code the change for you. I cannot speak on that with any authority.
An alternative is to use your printer drivers to accomplish your goal, though. Most modern drivers will allow you to add watermarks, and all HP printers, for example, have "DRAFT" as a built-in watermark. I know that is adding a couple of steps to your process, but it would help alleviate the problem until a more proper solution could be coded for you.
Cheers,
DrUltima