It all depends on what you would like to backup.
If it's just your important files, music and photos. The putting them on cdr should be fine.
If you want to back up your whole system, in case of a total crash or hard drive failure.
This is what I would do, so the computer can be up and running in minutes. This assumes you have a full disk and not a restore disk.
I would get a spare hard drive, say click here for £33. Install it as a slave drive. Then use the software to image the C drive to the slave drive. It will copy everything, even partitions, pro rata. It will be bootable.
You can then take out the slave drive and store it away from the computer.
If your hard drive fails, just take the old C drive out, put the slave in and boot up. You should be up and running in a few minutes.
You could even take out the old C drive and leave the new shiny 80 gig in. You would then have a fast 80gig C drive.