Just create it, When you need to use it you should check in the BIOS that CD is set to be the first Boot device that the PC looks for to boot from followed by Hard Drive.
PS you can before you start creating the CD try booting with the Acronic CD in the drive with it set as above, You can easy back out of it after its booted from the CD by removing the CD then Shut down by holding the Start Button in. This will not do no Damage as its only starting from the CD not the Hard drive.
If it will boot like that, you can create a Backup Image to another Partition or USB external Hard Drive if its plugged in Without loading it to your Hard Drive. I only create full Images for to Restore from not Incremental Backups, as this way Acronis will not mess up your Hard Drive Partitions