Lookup Fields and Forms - how do I control the combo box?

[computerider]

I have a standard two-table structure, Orders which has a lookup field to the Salesperson table. However when you build a form the salesperson field has the combo box feature - which I WANT when adding new orders BUT NOT when viewing existing orders (because you can actually change the salesperson by using it) - I am guessing I must use code (have no idea what code) and add it to a from so I can have a View orders form (which now displays salesperson as a locked text field) and an ADD orders form which the code is not attached to and therefore allows the user to choose the salesperson using the combo box.
Any thoughts?

[Rabbit]

You can lock a field in code by using:

Me.ControlName.Locked = True

[NeoPa]

Try an On Current procedure for your form :

Private Sub Form_Current()
  Me!Control.Locked = (Not IsNull(Me!Control))
End Sub

This will lock a field when it is selected and it has existing data, but unlock it if the field is empty.