As it sounds like you need to use CDR as the backup medium I would recommend DAR - Disk ARchiver http://dar.linux.free.fr. DAR is similar to suing tar & gzip but it can actually split the archive into pieces of arbitrary size called slices. I have used DAR to backup an entire linux partition & split the resulting archive into 645MB slices & then I used k3b to burn them to CD. I then repartitioned the HD & used dar DAR to extract out the filesystem. In your case you would archive the filesystem & then not put it back in the same place as it would overwrite your new working syste. I don't know if is included in the debian/knoppix package mirrors. At the time I was using Gentoo & I had to download & compile DAR myself. Here http://gradha.sdf-eu.org/textos/dar-...i-howto.en.htm is a howto on using DAR.

Good luck.
James