Ubuntu Install CD Customization
"The process of customizing or "remastering" Ubuntu install CDs is not especially complex, but it is a little tedious and finicky. This page documents all the problems you might find; if it doesn't, please edit it!
The Ubuntu install CD (since Ubuntu 6.06, the 'alternative install' or 'server' CD) has three main parts: a bootloader (ISOLINUX on amd64/i386 systems, yaboot on powerpc) and its configuration, which start everything up; debian-installer (also known as d-i), which in this case is really a specialised miniature Ubuntu system; and a Debian-style repository structure, which is what takes up all that space on the disk in the directories "pool" and "dists". Building a new CD may involve modifications to all three parts."