jrsitman,
You can install both, but if you switch back and forth between them you will be forced to endure the set-up routine multiple times. (Excel, Word, and PowerPoint 2007 co-exist more gracefully with their 2003 alter-egos; of course, you can only have one version of Outlook at a time.)
You might be best served installing the lesser-used version into a VM.
Patrick
