THe link below will take you to download entourage web services edition for Entourage 2008. It’s a free upgrade from Microsoft and will be required to use Exchange server 2010
It uses web services instead of webdav to retrieve your emails, calendar, etc
Prior to installing the web services update, ensure that you download and apply this update: Office 2008 for MAC 12.2.8 update
step 1: Ensure your mac OS is Snow leopard with all the updates
step 2: Apply Office for MAC 12.2.8 update. Link is given above
Step 3. Apply Web services update for Entourage
Step 4. After installation, launch entourage. Say yes to import your identity from old entourage.