How can one share Outlook Calendars?

I'm helping with a task to get 5 people all hooked up so they can see each others Outlook calendars. Now, I know you can do it with Microsoft Exchange Server, but are there any other choices? They are not on the same network either.

Also, can one edit someone else's calendar when they are on (or not on) the same network?

Any ideas?

Thanks

 

As far as I know it cannot be done easily, maybe try using some tools like the following http://www.slipstick.com/outlook/share.htm

 

Try SyncML. Free and Open Source.

 

Thanks everyone. I'm looking into the SyncML.