A family of Microsoft relational database management systems designed for ease of use.
I don't see any real harm in allowing them to use the navigation buttons. If the data is incomplete the code in the form's BeforeUpdate event procedure will kick in if they try, and prevent them leaving the current record until they've saved entered the required data.
You might also be interested in the SaveDemo.zip file in my public databases folder at:
https://skydrive.live.com/?cid=44CC60D7FEA42912&id=44CC60D7FEA42912!169
You might have to copy the text of the link into your browser's address bar (not the link location). For some reason it doesn't always seem to work as a hyperlink.
This file includes validation on the first and last name, but also forces the user to save the record and close the form via command buttons.