Dear Rico,

which Outlook versio are you using?

With Outlook 98/2000 maybe NetFolders could be a solution:
http://www.slipstick.com/outlook/share.htm#netfolders

With Outlook 2002/2003 NetFolders is no more supported:

On this site is an article on various ways to share Outlook data:
http://office.microsoft.com/en-us/assistance/HA011477571033.aspx

You will also find a list of third-party sharing tools:
http://www.mapistore.com/Outlook/Groupware
http://www.slipstick.com/outlook/share.htm

--
Oliver Vukovics
Share your Outlook without Exchange: Public ShareFolder
Notebook Synchronisation for Outlook: Public SyncTool
New Domain: www.publicshareware.com