How detect an active Direct3D window ?

[sirnoname]

Hello,
i want to detect automatical, when direct3d goes to foreground, fullscreen.
This means, if i start counterstrike or some other direct3d application that
i get a log entry. Is there a funktion to get an aktive fullscreen direct3d
window produced by any direct3d application ?
Or a funktion which gives me a handle to the applikation with this d3d window ?

regards
sirnoname