I still use knx-install, but suspect I may be in a tiny minority.

The part of the other install which seems to be problematic is the disk partitioning. You could use cfdisk from the CD to do that. Then use the knoppix-installer (choose the Debian option).

There's no need to make the XP drive bootable (and to do so may be dangerous). Cfdisk will let you choose what partitions (or drives) to modify, so used with a modicum of care, you'll be OK.

You have the labelling slightly askew. From what you're telling us, you have XP on the first hard drive (as primary master) = hda, and you want Linux on the second drive (the primary slave) = hdb. The digits after (for example) hda (hda1, hda2 etc.) refer to partitions. HTH