To Catch a Scrollbar

Hello.

Is there any way to catch the message that displays a scrollbar on a listbox, grid, etc?

For example: you have a listbox sized to display four lines comfortably. However, you then add a fifth line which causes a verticle scrollbar to be displayed. Is it possible to catch?

I still want the scrollbar to display, however, so turning off scrollbars is not a solution. I just want to be able to react to the creation of the scrollbar.

thanks,