Two days ago we got the defective notebook back from support.
Everything works as expected, no problems at all. They changed the mainboard and performed a Bios- and DVD-Burner-update.
My first tries with Knoppix 3.6 are somewhat successful. It seems to support the power-saving features but I failed with suspend/standby/hibernate. Reboots when coming back from those modes…
Well, perhaps things go better when Knoppix is lying on the HDD and not running from CD.