Hi Rob,
Mozilla Sunbird is a standalone calendar designed for use on a end user system. As there is no GUI to SME I don't think you will be able to run it on SME.
Perhaps you are looking at sharing the calendars between multiple clients of your SME. In which case I think it is something along the lines of DAV rpm you are needing to look at - which should allow you to store the calendar data from the server to multiple clients, however I have no experience with this to confirm.
Cheers, Shell