I have a highly customized desktop built from CentOS 5.4 and RPMForge repos (plus some stuff of my own). I'd like to build a LiveCD from that,
Did you try revisor? http://revisor.fedoraunity.org/
It is in EPEL and more or less work for CentOS.
Available Packages revisor.noarch 2.0.5.2-3.el5 epel