Hi, you *are* trying to copy CD's from an HDD-installed knoppix, right?
Otherwise, unless you have two readers/one burner, your cdrom is locked
because that's where knoppix itself is running from, and you probably cannot
acces it the same time for duplication purposes.
Just my guess, but I think it makes sense.
Other than that, KDE also has the cdbakeoven software, but I don't have a
3.1 knoppix copy handy to check whether that's included, sorry.

BTW, does someone know where I could download the latest, greatest,
stable and gnome-enabled 3.1 knoppix iso?