Yes, you will need to create a COM addin (start at http://www.outlookcode.com/article.aspx?ID=36)
You will be able to create a custom button on the Outlook ribbon/toolbar. Or you can just trap the Application.Inspectors.NewInspector event, check if the new item (Inspector.CurrentItem) is an appointment, and populate the AppointmentItem.Subject and the AppointmentItem.Body properties.