[CentOS] How the Centos 5.0's kickstart initrd.img is build??

Hi,

Any one know how the Centos 5 kickstart initrd.img was built? I'll be very appreciated if any light can be shed on this topic. The basic problem to be solved here is: how to build a custom vmlinuz+initrd.img for Centos 5 kickstart with my own custom built kernel?

I am not sure mkinitrd is the right tool for this purpose? If do, which are the modules I should include with '-preload' options? And if there are any extra files/steps I should include/follow for the initrd.img file? Not sure how the stage2.img is loaded by kernel after initrd.img is loaded and run. Please help.

--Guolin