Outlook – sharing

I use Office 2010 & Rackspace to share calendars, contacts, etc.  Set up to link 2 desktops and 1 iPhone.  I'd like to know to set up a calendar that won't be shared.  I usually have kept a separate calendar that relates only to me -- tax filing due dates, etc.  There's no need for this to be shared across both computers and the iPhone.  But even though I have set up two different calendars, both are being updated & shared across the system.  Rackspace says this is a problem that needs to be solved by Outlook.