tell application "iCal"
	tell calendar "Nuke This Calendar"
		delete every event
	end tell
end tell

This was the only way I could find to delete a calendar without having iCal send “notifications” to every person from whom I’d accepted a meeting invite. There was an option in earlier versions of iCal to “Delete without notification,” but that was removed.

Feel free to use at your own risk (I backed up my iCal calendars, and I also have TimeMachine running).