Attempting to set up Microsoft Exchange Mail account on iMac with 10.8.2 - MES is 6.5 (2003). Works fine with iPhone and iPad - just not on iMac. Any suggestions?

Our work place uses Microsoft Outlook 2007, but the server MES lists the exchange software as 2003 (6.5.78....). I have successfully set up my exchange account on my iPhone 4S and even my iPad (ver 1). However, I cannot seem to connect properly with my iMac 10.8.2 - keeps telling me it cannot log on even though I put in the same stuff that I did on the iPhone. Is there any hope of doing this? I really am just trying to sync my calendars, and don't care if the email is anywhere else but the iPhone. Our staff here doesn't know Macs at all, and so is of no help. Suggestions?