Outlook 2007 has improved calendar sharing using Office Online. If you prefer not to publish them on an Internet server and you have one machine running Windows Server, Windows XP or Vista, you can publish the calendar to your computer and share it with other user accounts or anyone on your network who uses Outlook 2007 or Vista’s Windows Calendar.
All you need to do is install IIS (Internet Information Server) on one computer and enable WebDav. With the correct permissions, all local users can access and publish calendars at http://computer_name/folder_name.
By using this method to share calendars, the calendars will be updated on a regular schedule and pushed out to the subscribers.
Published calendars will automatically update or check for updates once per hour.
For network use, install IIS on a machine that will be turned on either 24/7 or on longer than the others for best results.