CreateDialog and sending a WM_NOTIFY from it

Hello all,

Maybe a bit of an esoteric problem, but one I would want to have solved 
nonetheless:

I've got a program which puts up a settings dialog (using CreateDialog). 
From this settings dialog I would like to send notifications (WM_NOTIFY) to 
its parent.

The problem is, the NMHDR structure expects the "idFrom" field (the control 
ID) to be filled in, and I can't find it (IDD_SETTINGS, as provided to the 
CreateDialog call) stored anywhere. :-|

Question:

Is it stored anywhere in the dialog, and if so, where ?

Secondary question:

Will using SetWindowLong with the GWL_ID argument on a Dialog window create 
any problems (does anything else use that field) ?

Regards,
Rudy Wieser