Google Apps provided an automated tool http://www.google.com/support/a/bin/answer.py?answer=33561&topic=15894 which will help you to reset the google apps admin password.

You can also access your Google Apps admin password reset page by visiting the login page for your domain (example: http://www.google.com/a/yourodmain.com) and clicking on "I cannot access my account." if you get a message which says contact your administrator, then you are actually at wrong url. that particual url is users login page not the admin login page. please check url with the above one.