Debian-Installer: Modifying or customizing images
In some situations you may want to change something in the DebianInstaller. The most common case is when the kernel the installer uses does not support your hardware, but a later kernel version does.
Note that the installer is a fairly complex system and thus modifying it is not a trivial task. The links on this page may help you get started.
/CustomKernel - building images with a custom kernel
/CD - how to modify an existing CD image
Remaster Netinstaller image - Step by Step guide on how to integrate non-free firmware and preseed.cfg
Backported d-i images archive - Ready to use backported d-i images (including actual Linux Kernel etc.)
Custom driver image for etch when a driver is not yet available