Mkris9,
SBS 2008 comes with Exchange 2007, not Exchange 2010. The client encryption requirement shouldn't be an issue with the Outlook 2002 clients. You definitely can't use Outlook 2000 clients though because of how Public Folders work in Exchange 2007.
Provided you're on Outlook 2002 or higher you shouldn't have any problems and won't need to upgrade Outlook on anyone's computer.
MO