It has recently been brought to my attention that people are in need
of an explanation of how to modify the init scripts in their distros
to make the progress bar work properly. Obviously I can't provide a
soluton for every distro that is out there, but I can give you some
hints.

The most important hint is: have a look at the splashutils-gentoo
tarball and use the code from there if possible. This will make your
work easier, as many useful functions are already written and you
won't have to design them from scratch. Also, if you decide to use
my code, it should be easier to integrate any future changes. 

In splashutils-gentoo.tar.bz2 there are 4 files:

init-splash is the splash service handler that is put in /etc/init.d/
and run after all other initscripts, at the end of the boot process.
The file will have to modified to fit with whatever scheme a given
distro uses.

splash is a helper program that should be put in /sbin, it should be
possible to re-use it with little or no modifications (the paths to
/etc/conf.d/ might need to be changed to smth else).

splash.conf is the config file that is stored in /etc/conf.d/ on Gentoo
systems.

splash-functions.sh is sourced from the main rc script. It exports a
function called splash(), which is then called in various places in the
rc scripts to inform splashutils what services are being started/stopped.
The accepted parameters are listed in the comments in the file.

I hope this short explanation will serve as a good introduction :) Of
course you will have to get a look at the code if you want to make
sure it works in your distro, but it's always easier when has some
useful pointers from the very beginning. 

Feel free to mail me, should you have any questions about the details
of how these scripts work.