knoppix@Microknoppix:~$ su root
root@Microknoppix:/home/knoppix# mkdir /tmp/n900
root@Microknoppix:/home/knoppix# mount -o ro,loop -t ext3 /media/sdc1/SystemBackups/20101109-backup-optfs.img /tmp/n900
mount: wrong fs type, bad option, bad superblock on /dev/loop/0,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so