Assuming that we are talking VBA in Access, you could do this:
Use the click event of the combo box to open the other form. The value property of the combo box will contain the number of the selected item clicked upon. You can then inspect this in this forms Open event to decide which controls to render invisible or read-only. Something like
<pre>Select Case Forms!Other_Form_Name!ComboBoxName.Value
SomeControl.Visible = False
SomeOtherControl.Enabled = False
</pre> and so on.
Hope this helps.