If you are using Microsoft Entourage the following settings should be switched on to synchronize them with Mac analogues: Calendar, Address Book and Notes. Go to "Microsoft Entourage - general preferences - sync services" to activate them. Synchronization between MS Entourage and Mac applications will occur automatically, when these options are enabled. Thereafter start the synchronization process.
Notice, that Entourage calendar will create a new "Entourage" category in iCal to interact with it.
