Open your form in design view, and right click on the upper left corner of the form and call up the proreties for the form. Go to the events tab and choose OnLoad then hit the ellipse (...) to the right of this box. This will take you to the VB screen, now just type:
msgbox "Whatever you want to say here"
Then save it, Access msgbox's default to just an OK button.
HTH
Robert