Any sufficiently advanced technology is indistinguishable from magic...
This is in the very early stage of something which should become a howto to understand the build process of the Debian Edu (install) cd - please help to improve it. I will do so too, on my way to eternal wisdom and happyness 
- tasks comes from debian-edu svn
- wantedpkglist*.txt is generated from tasks
- wantedpkglist is given to debian-cd to populate the cd
- missingpkglist is generated by comparing the list of packages on the CD with the list of wanted packages.
debian-cd
the code for the version of debian-cd we're using is at /home/builder/src/debian-edu/src/build/CD-administrator/debian-cd
During every build it's patched by debian-edu/src/build/CD-administrator/patch-debian-cd with debian-edu/src/build/CD-administrator/debian-cd.patch
If you want to exclude certain packages from the cd, there is a exclude-etch list (also used for etch-test) in that patch.
famous last words
... and any technology distinguishable from magic is not sufficiently advanced!