As the Debian Sarge installation CD/DVD doesn't come with suitable drivers for the SATA chipset or the ethernet adaptor of the T43, I had to use a snapshot of Etch in order to be able to install without problems.
expert26 or kernel26ata-piix, then let the installer detect the optical drive, then at the next prompt for modules to enable reenable ata-piix1) (This might seem a little bit weird, but is important in order to make the installer able to detect the optical drive at all)After this, just follow the normal installation process.
Kernel 2.6.14 needs some patch in order to properly work on the T43:
/dev/sda, and a hdparm -I /dev/sda reports an error. Applying the patch enabled S.M.A.R.T. and also the info output of hdparm.