GMAN,
The process is convoluted, but possible. Basically you can’t use the File | Open | other users folder. You have to open the Tools | Account Settings | then go to the more settings area and on the second tab you can add other users to your email. Add the user you want to share your subfolder under your inbox with. But, before you do that you have to change some permission settings. First go to the Inbox that has the subfolder you want to share and give the user that you want to share it with “View Folder” permissions, and then under the subfolder give whatever permissions that suite your need.
Thanks to the following email for jogging my mind on this.
http://www.princessfixit.com/archives/000123.html
Always there for a helping hand,
Robi