Apple Mail for OS 10.6 and OIT's Exchange service go hand in hand.
To make sure your iCal is configured properly for Exchange follow the steps below.
If you cannot connect to Exchange and you have SecureMac (OIT provided application package that contains Fetch and terminal shortcuts) installed on your computer, you need to delete a file on your computer. Click here to find out how.
Click on Accounts.
In Accounts make sure your Exchange account is highlighted and then click on the Server Settings tab.
Make sure that your iCal is configured with settings like those seen below.