DVD drives are dirt cheap, I can't argue against simply installing one. About $15 for a burner from a source like Newegg. You said reader; readers may be even cheaper but I can't justify buying only a reader. Get a burner and burn your own DVD at low speed for the best Live DVD experience. And it will be handy for many things. But if you want a fix to your problem that you can start doing right now, you could try installing Debian today while you are waiting for the DVD drive to arrive. If you don't like it you lose nothing and can switch back to Knoppix or some other Live DVD after you have the drive. But you really didn't answer the question of why you seem to be resisting Debian and are focused on Knoppix, which is intended primarily as a Live DVD, while ignoring Debian which is intended for had disk install. You're hardly alone at that, as I never seem to get a good answer to that question.

Oh, one thing to mention. Just about any internal DVD drive that you buy now will have an SATA interface. Your PIII system with CD sounds like it has IDE interfaces. So if you don't have a SATA adapter in that system you'll have to be creative. You can't use a USB external DVD drive, USB 1 or USB 1,1 are not going to cut it. SCSII DVD burners will be very hard to find and you will likely pay such a premium to get one that you would be better off just buying a "new" $100-$200 computer that had a DVD and a lot of other things that you really need. Or find an old computer with IDE that you can pull the DVD drive out of, or simply get something a bit newer. If you decide to try to add an SATA adapter be sure that it has an interface that your motherboard supports, PIII is very old and you might not even have PCI sockets on it.

All of which makes the suggestion of just trying to install Debian from the Internet a much more viable option.