How do you reference control objects from a modal form ?

Hi
I'd like to know what the syntax is for referencing a textbox on my activex
control from a modal form that is launched by the control. i.e. I have a
popup form where you make a selection from a listbox and click on OK, the
selected value must then be written to a field on the usercontrol.

PLEASE NOTE: I'm trying to write a value from the form to the control and not the other way round.

Thanks

Uthmaan