One of the items overlooked so far could be the system bios. I found on my test box that even after making a new partition and placing knoppix in the root of the new partition (fat32) that knoppix will not boot because the older bios does not see past a set number of gigabytes from the boot sector of the drive. Using a modern os can overcome the problem because it does not have that limitation. But since the disk is filled up past the point the bios recognizes, it will not see the other os.

My original problem was with a dell optiplex gx240 with a 120 gig drive.