[CentOS] How to setup VNC for GDM access on 6.3

Hi all,

I'm looking for pointer for setting up VNC so that access to the system is via gdm/kdm.  Yes, I know about vino, and /etc/sysconfig/vncservers but what I'm looking for is a sertup 
that allows me to see the *dm login screen instead of being dropped direct into a desktop.

Thanks in advance