how to attach a pixmap as windows background?

[Jiang XU <jiang xu echostar com>]

I try to attach a pixmap (declare as GdkPixmap *) as the background
picture of the top level window (or pop up window, or dialog),so that I
can put other widgets in the window without affecting the background
picture.  But I don't know how to attach the pixmap as the property
(background) of the window, so need help!

If anyone knows please teach ASAP!

thanks very much

John