The impetus for this quick tutorial was a post on the MacBites shownotes site from Gazmaz. We’d mentioned our requirements for sharing calendars and Gazmaz wanted to know if there was a way to share calendars on the same Mac but in different user accounts.
After some pondering I gave the following a try and it works perfectly … hope you find it useful.
Accessing BusySync Preferences

BusySync doesn’t have a program interface, it is controlled via a Preference Pane within the System Preferences.
Clicking BusySync displays the required Preference Pane.
Publish the Calendar/s

Click the Publish option to display the iCal calendars available for sharing belonging to the currently logged in user.
Add a tick to those calendars needing to be shared.
Specify Required Security Settings

Additional security options are available by selecting a calendar and clicking the "Publish Options…" button.
In the displayed dialog a Read only password can be specified and/or a Read and write password can be specified.
The same passwords will be used for all users – passwords are not created on a per user basis.
It is possible to share a calendar without specifying a password, just leave both options blank.
Enable Fast User Switching

The next step is to enable fast user switching via the Accounts options in the System Preferences.
First, click the "Login Options" (1) and second put a tick in the "Enable fast user switching" option (2).
Accept Security Warning

When you attempt to exit the Accounts section of the System Preferences a Warning will be displayed explaining that the option you have just enabled will allow other users to stay logged in and run applications while you are using the computer.
This is necessary for the BusySync calendar sharing to function.
Fast User Switching Menu

Once you have accepted the Warning dialog the "Fast User Switching" menu is displayed in the top right of the menu bar.
The next step is to log in as the second user in order to subscribe to the published calendars.
Click the name of the required user.
Log in as Second User

Enter the password of the selected user and log in.
Subscribing to Published Calendars

In the BusySync preferences within System Preferences click the Subscribe option to display the iCal calendars available for sharing.
Add a tick to those calendars that you require access to.
If a password is required this can be entered via the dialog displayed when the "Subscribe options…" button is clicked.
Switching Users

Once the Subscription has been created you can switch between users using the "Fast User Switching" menu in the menu bar.
Subject to permissions both users are now able to manage the shared calendars.
Where to Get BusySync

BusySync is available from BusyMac.com and costs $19.95 per seat (an introductory offer).
The BusyMac site also includes an FAQ section, a blog and a video tutorial.