Setting the root window with GDK

[Tilman Sauerbeck <tilman code-monkey de>]

Hi,
I'm trying to set the root window using the routines offered by GDK.
However, it doesn't work at all :/

What I'm doing is:
* calling GDK_ROOT_PAREN() to get the root window
* loading some file into a GdkPixbuf
* rendering that pixbuf into a pixmap
* calling gdk_window_set_back_pixmap() and gdk_window_clear() to
  actually set the background and redraw the window.
  
Steps 1-2 work, I'm pretty sure step 3 does so, as well (at least I
checked whether the returned pixmap was NULL), so it must be the last
two calls that are failing, IMHO.

I got some sources off the web which are doing almost the same, but
I just don't know what's causing my code to fail.

Can someone enlighten me please? 

I'm using GTK 2.0.9

Thanks in advance,
    Tilman