[CentOS] Loading GNOME with GDM

Hi,

We have a few PC with CentOS 4 installed.
By default, it runs to runlevel 5, which displays the GDM.

I'm just wondering, how do I actually make the GDM to start GNOME
automatically (after a successful login) for all normal user account
without having to add 'exec gnome-session' in every user's ~/.xinitrc?

The current scenario is, only successful 'root' logins starts the
GNOME, while other normal user successful login is presented with the
minimalist window manager (which is equivalent to 'Default System
Session' from the GDM menu).

I'd appreciate if anyone could help me to figure this one out.

Thanks!

-Ikmal