I admire your perserverance. It has been my experience that zeroing the entire drive, then partitioning and formatting your partitions is a good idea especialy if you had windows partitions. So I would do this:

Boot Knoppix
open a terminal and get root
dd if=/dev/zero of=/dev/hda

This will take a while. A long while. You'll get an 'Out of diskspace' error when it's done.

Of course you want to be sure that /dev/hda is the right drive or......

Install XP
DO NOT let XP use the entire drive- only what you need.
You may want to create yet another partition to share between Knoppix & XP.

Install Knoppix

Rule of thumb. It is best to make win partitions w/ a win partition utility and Linux partitions w/ a Linux utility.