For a company events calendar, you can simply create a new Calendar folder in Public Folders and grant permissions through the Properties dialog for the folder.
Outlook 2007 adds the ability to send calendar files and publish your calendar for sharing. This supports just one way sync – the sender can update the calendar but others can't. If all users need the capability to update the calendar, you'll need to use one of the tools below.
Tools in the Spotlight
Gives managers, secretaries and co-workers an instant, web-based view of where people are, what they are doing, and when they are next available. AgendaX will seamlessly manage multiple time zones and allow global views of staff availability and resource allocation. AgendaX incorporates many features that allow you to take advantage of Outlook calendaring, Active Directory attributes and web views to give you the ultimate corporate resource portal. No client installation necessary and nothing is installed on Exchange Server. Supports all Exchange Server versions. New Version 6 available now!
Use Add2Exchange Enterprise Calendars to synchronize Exchange public folder calendars to users so they have a local copy of appointments and for viewing on their smartphones. Automatically copy appointments created in your public folder calendars to mailbox folders for a public to private sync. Sync new appointments in users' mailbox folders to public folders for a private to public sync, and/or sync calendars between users' mailbox folders for a private to private sync. Sync 1-way, bi-directional, or a 'full mesh'. 21-day trial available
Sample Outlook form application to maintain a central calendar. (Microsoft Office Update)
For additional information on group calendaring, see Maintaining a Group Calendar in Outlook