If the form is in single form view, not continuous forms view, then, yes,
you can use VBA code on the OnCurrent event of the Form and on the
BeforeUpdate event of the control. If the Conditional Formatting isn't
enough, check MVP Stephen Lebans' site,
http://www.lebans.com -- he has some
workarounds that might give you more flexibility (they were created for
Access 97 or earlier, where there was not yet Conditional Formatting in the
product, but might be adaptable).
Larry Linson
Microsoft Access MVP