How to upgrade Debian 3.1 Sarge from kernel 2.4.27-2 to 2.6.8-3

The machine for this guide was an IBM xSeries 206 with SATA. The problems arised from the different addressing of the SATA system - in the old kernel the first SATA disk was recognised as /dev/hdc, while in the newer ones it was /dev/sda

We start with a

aptitude install udev

after that you have to edit in /etc/mkinitrd/mkinitrd.conf the ROOT line to the root of your system and MODULES line to "most"

ROOT=/dev/sda1
MODULES=most

create /etc/mkinitrd/files with the following entries

/dev/console
/dev/null
/dev/hdc
/dev/hdc1
/dev/hdc2
/dev/sda
/dev/sda1
/dev/sda2

the mandatory entries are /dev/console /dev/null and the lines for the disk and partition where the OS resides. After that we install the kernel image with aptitude install kernel-image-2.6.8-3-686 and check in /boot/grub/menu.lst that root= points to the correct root partitions on the right device.
To stay on the safe side we can also check the initrd image with

mount -t cramfs -o loop /boot/initrd.img-2.6.8-3-686 /mnt

we check in /mnt/dev for the correct devices, /mnt/loadmodules for the ata_piix module and /mnt/script for the root location.

That should be it. Cross you fingers and reboot.