You'll need to either purchase an Exchange Server, or find a third-party application to enable group calendaring. I'd suggest you start by doing some searches at Slipstick.com for starters.
Do you have comments on this Ask the Expert Q&A? Let us know.
Related information from SearchExchange.com:
Dig deeper on Microsoft Outlook
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.