I had the same trouble with the hard drive install. Here are the steps that I did:
1. I booted the Knoppix CD
2. I mounted the partition where Linux was installed during the knx-hdinstall as read-write (right click on the disk icon, select Properties, then Device, and de-select "Read only")
3. I located the /etc/shadow file on the partition (be sure that it is the one on the hard drive, not the CD)
4. I opened up a root terminal (under the K menu>KNOPPIX)
5. I typed "kedit /mnt/hdax/etc/shadow" (where x is the hard drive partition)
6. The first line was root. I deleted everything between the first two colons (":"). That is the encrypted password.

The line will now be "root::0:99999:7:::"

Logout from the CD and remove it. You can now log into root leaving the password blank. When you are in root, open a terminal and type passwd to change your password.