I recently had to renew my Exchange certificate as it expired. The original admin that set up this Exchange bought the previous certificate from Digi. I decided to go with Startcom (Free SSL) as I have used them once before in an OCS deployment and they worked out well. Exchange is a little different in that you must use Exchange management shell (PowerShell) during the process of installing a certificate for Outlook Web Access (OWA). I am going to cover 5 steps to installing a certificate Exchange for OWA.
To Open Exchange Management Shell: Go to START >>Programs>>Microsoft Exchange Server 2007 >> Exchange Management Shell
This is the management shell