A knx-hdinstall will wipe out your existing install and re-install from scratch, if you have your partitions in order you won't have to re-do them. Just make sure while the system is still in tact that you figure out what linux partitions are being used by your knoppix install, so you don't do something to mess up your system, then just select the proper partition(s). It's been quite a while since I've done a knoppix knx-hdinstall, so I don't remember all the details, but if you get dropped into cfdisk and everything is OK just exit it, and the installer should continue on its merry way.

Note: if you've done any customizing that you want to save, ie: edited any scripts, have a home directory that you would like to keep, bookmarks, emails, etc. make sure to save those before you do the re-install.

rock