You cannot import the calendar data from Outlook to Entourage X. Both programs use different systems. Outlook uses the Exchange server to hold the calendar information which can be shared or amended with other users. Entourage X calendar system is PIM or Personal Information Manager, which is used by hand held devices.
Unfortunately, at the time of writing, Entourage X does not support PIM with hand held devices.
Importing the calendar imofrmation from Outlook Offline folders and files will not work either.
There might be a third party solution software out there on the web, but I would not hold my breath.
Sorry to be the bearer of bad news.