Simple way to create an ISO image of your disc in Ubuntu...

Go to Terminal:

sudo umount /dev/cdrom
dd if=/dev/cdrom of=filename.iso bs=1024

To verify your ISO file is good:

md5sum /dev/cdrom
md5sum filename.iso

Both instances should produce the same md5 hash. :)

Note: "filename.iso" is only an example filename, feel free to use any name you want.