With the information you've given us, I'd say the only way would be thru the use of MAGIC!
The very general way is thru the use of the AfterUpdate event of the first textbox:
Code:
Private Sub CountryTextBox_AfterUpdate()
If Me.CountryTextBox = "United States" Then
Me.Flag = "Stars and Stripes"
End If
If Me.CountryTextBox = "Canada" Then
Me.Flag = "Maple Leaf"
End If
End Sub
I you have a lot of possibilities for the value in the first textbox, you might want to use the Select Case construct instead of using If...Then...End Ifs.
If you can give us a bit more information on what you're trying to do, myself or someone else here will be glad to help you further.