Sharing a Calendar from Mountain Lion server with Snow Leopard users on local network

Hello.

I have a new Mac Mini Server running Mountain Lion Server and I want to create a shared calender for a mix of Lion, Mountain Lion and Snow Leopard users on our local network. Does anyone have any info on how to do this? I have tried using the Server App and Calender Help within the applications, but the content isn't available. I have managed to create a Shared Calender from the Mini's Calendar App where I've added users and I can see a 'wireless' transmit icon to the right of the Calendar name - but I cant get any of the users' iCal or Calendar apps to recognise the Calendar on the local network. I've also created a Location in the Server App under Calendar and still can't see anything on the local network. Am I missing something really obvious?

Thanks in advance!