Good news! There's a special version of Knoppix, made just for install to hard disk! This special version avoids the apt-get update problems of disc based Knoppix as well as the many things that often work on the CD but stop working after a hard disk install. And it has all of the Knoppix software available and a much larger pool of additional software too, and you can pick what to install and what not to install, saving space. Many GUI front ends are available to pick from, not just the ones included on the normal Knoppix CD (although KDE is certainly available). Software updates are available faster than waiting for a new Knoppix CD and updates don't break everything else when installed.

And, of course, it supports all the user log-ins that you want.

This special version of Knoppix is called Debian. You can get a copy of it here. I suggest getting the net-install or business card versions of the i386 version, or a 64 bit version if you have the CPU for that, and installing the rest from the Internet.