You can't boot a HDD as a DVD or CD, due to different filesystems. You could possibly copy all the files with
rsync and burn a DVD/CD with all the files, but you can't just
dd a HDD image onto a DVD. You could use
dd to copy one hard disk to another, and the second hard disk would be bootable, though.
On the other hand, you can try
genisoimage (cdrkit, of the debian project) or
mkisofs (cdrtools, which is what debian forked). I've used genisoimage to make bootable discs before, like when I copied all the files from a debian disc, changed a few, and remade a .ISO. It might not work for windows and some other OSes, but it's worth a shot.
I did my bootable CD following this page: