You need to set the GDM/KDM to login using LDAP authentication instead
of local.

Install the ldap admin modules and use them to set it up.
(Sorry, can't be more specific, it's a long time since I did it on
RH/Fedora)

On Thu, 2011-09-08 at 09:20 -0700, Christopher Tooley wrote:
> I have the option to do LDAP with a centralized server, and I would
> like to do so.
> I use NFS mounted home directories (NFSv3).
> 
> I have installed SL6.1 and it works great.
> 
> I know I have successfully set up LDAP *and* NFS, because I can log in
> remotely with SSH as well as on a terminal.  However, when I try to
> log in with GDM or XDM, it will accept my password, black out the
> screen, and then return to either GDM or XDM.  I *can*, however, log
> in with a local account.
> 
>