Bob Berwick ( http://lists.debian.org/debian-boot/.../msg00639.html )
has reported a succesful installation of linux on a Dell 8400 right out of the box:

Bob Berwick wrote:
"Red Hat released Update 3 of their RH Enterprise System Version 3 linux.
This Update 3 patched the ata_piix driver so that it *does* handle ICH6.
It can boot and install RH linux successfully on my Dimension 8400, properly recognizing
the drive partitions as sd* (rather than hd*).
'doze even dual boots."

Thus it should be possible to get it running on knoppix, etc.. too.

Will first need a backup and then give it a try.