How to get the gtk widget's ...?

[Duncan Chang <DuncanChang via com tw>]

I had a question to need your help.
My question is described following:
I can get the widget handle from the gtk_window_new(), but how do i get the
window handle(like the return value from 
XCreateWindow()) from the widget handle, because i need it to pass as an
parameter in low-level x-lib API.

Thanks!