The occurence and functions of ARCalender can be changed using the configuration dialog. The options shown there represent the registry tree under "HKEY_CURRENT_USER\Software\ARCalendar".
The options of the configuration dialog are currently not documented. It is not recommended to change any settings without knowing what it does.
The configuration settings are organized in categories. If you open one categoriy two columns are shown. On the left is shown the name of the option, while on the right you can change the setting. If options are shown in italic, they can't be changed.