Access 97 Form & SubForm

I have a Main Form called "Membership". ON IT, is a subform called "ALLDUE subform".

On the Main Form (Membership), each time I add a new record I want to:

1) move the focus to the Year field on "ALLDUE subform". I HAVE DONE THIS!

2) If no year is entered (on the sub form) when you try to go to a new Parent record, or save this Parent Record, a message "No Year has been entered" should pop up in a Messsage Box and cancel both the Subform changes as well as the Main Form changes.

Does anyone out there have any ideas on how to accomplish this?

Thanks,
Alan (abramowitza@coned.com)