CentOS - Oct 2008 - How to create custom CentOS5.2 iso?

Hi,
I am very new to this community. 
I want to make a custom iso which contains CentOS5.2 & scopserv(asterisk
based PBX). Please provide me the proper steps for creating an iso.
I have created an iso but during installation, only CentOS5.2 rpms get installed
& scopserv rpms doesn't install.

Is genhdlist command is required? But this command is not working with latest
anaconda-runtime version i.e. anaconda-runtime-11.

Please help me as I am stuck somewhere.

Thanx in advance.

Manoj Kumar