Only one Outlook instance can run at a time, so that's easy. Just check for
Explorers.Count and Inspectors.Count, depending on what types of UI you are
looking for.

Signature
Ken Slovak
[MVP - Outlook]
http://www.slovaktech.com
Author: Absolute Beginner's Guide to Microsoft Office Outlook 2003
Reminder Manager, Extended Reminders, Attachment Options
http://www.slovaktech.com/products.htm
> When in the context of a COM addin is there a way to know whether your
> specific outlook instance is an outlook GUI instance or a non-gui
> instance?
>
> Dave