(defun my-insert-dates ()
  "insert a bunch of dates"
  (interactive)
  (let* ((month 3)
         (day 1)
         (time (encode-time 1 1 0 day month 2009)))
    (while (= (nth 4 (decode-time time)) month)
      (insert (format-time-string "%D %a:n" time))
      (setq day (1+ day))
      (setq time (encode-time 1 1 0 day month 2009)))))

(require 'calendar)
(defun display-a-month (day month year)
  (insert (format "%sn" (calendar-date-string (list  month day year))))
  (if (< day 30)
    (display-a-month (+ day 1) month year)))

(defun my-insert-dates ()
  "insert the first day of each month"
  (interactive)
  (dotimes (mo 12)
    (insert (format-time-string "%D %a:n" (encode-time 1 1 0 1 (1+ mo) 2009)))))