Restoring from a mondo backup is easy; simply burn the images, put it in a cd drive and nuke the system (yes, this is a restore option in mondo :) ).
If you just want to restore some files from the backup, without overwriting the whole system, there's an easy way to do this. Suppose you created an ISO a while ago and these are stored on some disk. First, you will need to mount the ISO as a loopback device like so:
mount -o loop MyIso.iso /mnt
The ISO is now mounted in /mnt.
Now locate the file you want to restore (I was going to restore smb.conf):
$ grep smb.conf /mnt/archives/filelist.*
The file I needed was somewhere in an archive identified by number 5.
Now create some folder in a temporary location:
$ mkdir /tmp/restore
$ cd /tmp/restore
Now restore the contents of the archive you want (you might need to download and install afio):
afio -ZP bzip2 -i /mnt/archives/5.afio.bz2
The whole archive is now restored underneath /tmp/restore. So my smb.conf is now located underneath /tmp/restore/etc/samba/smb.conf. Pretty cool eh.
Anyway, I don't deserve any credits for this post, I found a lot of help here.
EDIT: Apparently there is an easier, more graphical way to restore stuff from a mondo archive.