If all you need is a disk image, not a disk clone, then the built-in disk utility can create it for you, but it will be bigger than a DVD in size. Perhaps Toast can span it to multple discs. I don't know how you would go about resoring the multiple discs if you ever needed to do so. I use SuperDuper! to create a bootable clone on an external hard drive, and have found this so much more useful than the old disk image that I was used to on Windows (Norton Ghost, Drive Image, etc).
