A client of mine purchased one of the new iMac’s and needed it setup on the network. Specifically, they wanted Entourage from Office 2004 for Mac to work with their exchange server. After following the setup wizard and putting in the proper server settings it still would not work. After searching numerous sites without any luck, I came across SimultaneousPancakes. There is an older post from January, 2005 that had my answer. Apparently, Entourage connects to Exchange using Outlook Web Access, quite similar to Evolution actually.
You can find the step by step instructions on the original page which is located here.