Sherweb Hosted Exchange - Trouble Sharing Calendars

We use a Sherweb hosted Exchange server and use Apple Mail, iCal and our iPhones to access our contacts, email and calendar information from the Exchange Server. The Exchange setup with Snow Leopard worked well (we're able to access our contacts, email and calendars using the built in Apple programs). However, I can't access the shared calendars of other users in our Exchange Server. It works well when I use Entourage, but I would prefer to use iCal to access the shared calendars. Has anyone had any luck getting iCal calendar sharing to work with a Sherweb hosted Exchange server? I think that the default server settings the Snow Leopard put in place aren't allowing the shared calendars to work properly. Any ideas?

Thanks for your help.