Enable/Disable an Edit Control box in Property Page

Hi,

I am working on Property Page of a filter.
I have added a ListBox in the property page to hold items for video
resolution.
Among the items in the list, there is one item called User Defined.

I am trying to get a functionality where in, if I select User Defined
in the ListBox, this selection will enable 2
Edit Control boxes so that the user can fill in Height and Width.

Now, if I deselect User Defined and select some other item in the
ListBox, the Edit Control boxes should be disabled.

How do I do it programatically in the OnReceiveMessage() function?

Please let me know.
I have been trying to enable the disabled Edit Control Boxes using,

SendDlgItemMessage(hList, IDC_RATE3, WM_ENABLE, (WPARAM)TRUE, 0);

But this does not work.
Thanks,
Taklu

Create member variables for the controls and use CWnd::EnableWindow()