It depends on the version of Outlook. They used a sharing method called "NET FOLDERS" that works pretty good, but it does have some problems which is why I guess they removed it in the newer versions of Outlook. Net Folders would update subscribers by sending special emails. The help text will explain how to set it up and there are plenty of places on the Net to get help now that you know the key word to search for. Here is a link that might help:
http://www.slipstick.com/outlook/share.htm
Personally, I would use an email product like IMail that has a web calendar and then use LDAP for the contact sharing. I have an IMail Server setup if they need a virtual mail server for their domain or want to setup a domain for email and contacts. The hosting cost is $20/month for unlimited emails and the web calendar is included.