how to create a window haven't title bar and not show in tasklist

[huzheng <forlinux 263 net>]

i use: 
window = gtk_window_new (GTK_WINDOW_POPUP); 
but this window always on the top 

then: 
m_MainWnd = gtk_window_new (GTK_WINDOW_TOPLEVEL); 
gtk_widget_realize (m_MainWnd); 
gdk_window_set_decorations (m_MainWnd->window, (GdkWMDecoration) 0); 

this haven't title, and not always on top 
but,it show in the tasklist (in gnome)

is there a perfect way?