When you insert a CD into your Mac, I wonder what sort of Mac it is and what version of OS X it is using, it should appear on your desktop, assuming you have Finder preferences set to show mounted disks and CD's

Double clicking that should either open it, to view the files, or will launch the installer program.

However, I note you say that your "mac software version is correct" and that your printer is a 7520, but, your use of the term "iDisk" would indicate that your version of OS X is much older than the requirements for this printer.

You must be running OS X version 10.6 or above (Lion and Mountain Lion) to be able to install this printer.

Can you confirm that this is actually what you are running?