I've found an .rpm with drivers from Adaptec. I converted it into .deb with alien.
Tomorrow, I'll install an additional harddisk (ATA), make a Knoppix hd-install and hope that the above mentioned .deb will work.
Alternatively, I will try to use kernel 2.6.5.

If someone has already tried the above, or if someone has a better idea, please let me know! thanks. Juerg