You can connect to a SharePoint Calendar through Outlook 2007 or 2010. This will enable you to add and delete appointments from the SharePoint Calendar in Outlook 2007 or 2010.
To learn more about connecting to a SharePoint Calendar through Outlook 2007 or 2010, visit: http://office.microsoft.com/en-us/outlook/HA100819871033.aspx?pid=CH101032731033
This option is not available for Outlook 2003.