Center window on dual screen

[Yann Renard <yann renard mailing-lists aliceadsl fr>]

Hello,

I would like to get a window centered on one screen on a dual screen 
setup. When I use GTK_WIN_POS_CENTER, the window appears on both screen. 
I use GTK 2.12.11 with libglade 2.6.2, but a quite old gnome 2.10.0 
(don't know if the window manager should be responsible for this or not)

Best regards,
Yann