First of all I don't know if I read it right, but logging in as root and the su'ing to a user account "isn't the way it works". You should login as a user, and only su to *root* when necessary.

Now I don't have a solution for you probs, but if you add the "debug" statement in pam.d/su you'll get more output in the logs; maybe that can help track down what's going on.
Usually PAM modules will support the debug options but I haven't checked the online PAM docs if every one of em does.
Adding <space>debug to the end of each line enables it. Log out and log in, and look in /var/log/messages.

Btw if "identd" is broken just stop loading it with ntsysv, linuxconf or change the "S" to a "K" in your current (/etc/rc.d/rc*.d) runlevel.

i myself follow that rule of su'ing only when necessary but it was not allowing normal users in.....
tried adding debug to end of lines but no new message was there in /var/log/message.......
will try your suggestion on identd.....but can any one tell me what it's used for??.....i suppose
it must be used by su in someway.......
Thanks

I use SU everyday to mount drives which I have yet to learn how to automatically mount my mp3 drive on startup :x

man fstab

also see manpage of mount to know about various keywords
to use in fstab

Thanks!