I've been invited to a meeting - I am not the organizer. Is there any way for me to add another attendee, other than out-of-band communication?
Open your appointment in Calendar (double-click on appointment) and then click on Forward. You can forward the invite to your collegues; the message will be in this form:
Header: "YourName" on behalf of "OrganizerName"
Cc: Organizer of invitation