I would like to use a cmdlet to edit the Calendar permissions of a handful of users. (Reviewer permissions) Is this possible do to via the Management Shell, or do I have to use a tool such as PFDAVAdmin? This is just for scenarios where I do not have access to their Outlook client.

Hi,Use pfdavadminLeif

Agree with Leif. If move to exchange 2010, you can do it via EMS New Mailbox and Recipient FunctionalityJames Luo TechNet Subscriber Support (http://technet.microsoft.com/en-us/subscriptions/ms788697.aspx) If you have any feedback on our support, please contact tngfb@microsoft.com