Shared calendar with multiple platforms

We are a small company with everyone using a different OS. How can we use google calendar as a soution for a shared calendar when some people use entourage?  I know you can create a separate calenday and share it to your own personal gmail calendar but you have to micromanage what you share, how can I make a seamless solution that will sync our iPhones, blackberries, outlook and entourage using a shared google calendar?