Before you trust your backup CD, make sure your BIOS can boot CD (and that it is configured to do so).
Boot from the first CD.
Follow the on-screen instructions. This will compare your backup against your original file system.
FYI, no bad archives have been created since May 2000. Having said that, I would still encourage you to run Compare before trusting the backups.
To view the file differences, look at the file '/tmp/changed.txt'. Normal differences include logs and other dynamic system files that changed during the time of the backup process. If only a few files differ - e.g. files in /var, files ending in '˜', logs, temporary files, /etc/mtab, /etc/adjtimex - then you know the archives are good. Your logs will change over time, too. Bear in mind that a difference between the backup and the live copy does not indicate a flaw in Mondo. It indicates that you or your filesystem changed the files, so the backup is no longer 100% up to date. However, that is inevitable, as your filesystem changes from moment to moment (which is why you back it up regularly).