"In my experience I almost never need the install CD except during the initial install and as a bootdisk, so I just store the on-disk backup as an ISO rather than a logical copy of the files on the disk.
You can use any CD/DVD burning software to burn the ISO to a new disk. (You can use the same software to get the ISO in the first place, if necessary)
You could use daemontools or the like to mount the ISO directly if you need something from it without putting a physical disk in the drive."
