How do I grant permission for people to create top level public folders?

A. By default all users can create top level folders however this can be changed if you would like to restrict this

Start the Exchange Administrator program
Expand the site and select Configuration
Select "Information Store Site Configuration" and select Properties from the File menu
Select the "Top Level Folder Creation" tab
You will notice that under "Allowed to create top level folders" All is selected by default. Change this to list and click the Modify button
You will be shown a list of Exchange mail boxes, select the ones that should be allowed to create top-level folders and click OK
Click Apply then OK

Click here to view image
- Setting top level folder creation access

Alternatively you could have left is as All and modified the list of people who should not be able to create top-level folders.

If people are still logged in they will be able to continue to create top-level folders until they close Outlook/Exchange and restart it.