adding linuxrc to initrd

I need some help in modifying the initrd on installation DVD of one of
the distributions it does not have the linuxrc script by the same name
rather it has linuxrc.conf file
and an init script which I guess is the same as the linuxrc because
without it I can not start installation ,I would like to know how to
create a initrd file that has linuxrc also if some one can point to
sample linuxrc
and any documentation for making initrd from scratch (ex busybox etc)
not from the mkinitrd script that works that would be great.


as on man pages of initrd
http://www.netadmintools.com/html/initrd.man.html


What I understood is executable /linuxrc determines what is needed to
(1) mount the normal root file-system (i.e. device type, device
drivers, file system) and (2) the distribution media (e.g. CD-ROM,
network, tape, ...). This can be done by asking the user, by auto-
probing, or by using a hybrid approach.

I want to be able to create an initrd which I can give to my friend
who can start installation from it . by mounting root on cd or dvd
etc. Starting from scratch.