The default in RHEL 5 is to install bind chrooted
If you have installed the bind-chroot package, the BIND service will run in the /var/named/chroot environment. All configuration files will be moved there. As such, named.conf will be located in /var/named/chroot/etc/named.conf, and so on.
I can see you have installed the chroot pkg
bind-chroot.i386 30:9.3.4-10.P1.el5 installed
Incidentally, your system is not registered with RH, so you won't get updates or support.
You either need to pay & register, or replace with the same version of Centos; your choice.