If you save copies of some or all of your partitions individually, and want to be able to use them to restore a working system, you'll also need to backup and restore the MBR and partition table. (The same caveats apply as discussed above about whether partition tables can be restored onto a disk of a different size).

Backing up the MBR:

dd if=/dev/hda of=backup-of-hda-mbr count=1 bs=512

This stores the first 512 bytes of the disk (contianing the MBR and the primary partition info - i.e. the first four primary entries) into the file "bcakup-of-hda-mbr" which you can then copy to somewhere safe.

To restore (be careful - this could destroy your existing partition table and with it access to all data on the disk):

 dd if=backup-of-hda-mbr of=/dev/hda

If you only want to restore the actual MBR code and not the primary partition table entires, just restore the first 446 bytes:  dd of=/dev/hda if=backup-of-hda-mbr bs=446 count=1. (Those first 512 bytes are 446 bytes of MBR, then 64 bytes of primary partition table).

Backing up the extended partition table

sfdisk -d /dev/hda > backup-hda.sfdisk

(sfdisk is in the util-linux package. I think it's in Knoppix.)

Restore (ditto the above warning):

sfdisk /dev/hda <backup-hda.sfdisk

(then reboot)

 I also recommend making a record of the partition table details as displayed in whatever disk partitioning program you like to use, and also as displayed by fdisk -l. Could be handy if you find yourself needing to repartition the disk by hand in preparation for restoring some images of individual partitions.