It can be done easily. You may just be able to make an image of the disk in Disk Utility and then burn that image to a DVD-R.
If that didn't work for some reason, search versiontracker.com for DVD Backup. That will copy the contents of a DVD to your hard drive. Then search for DVD Imager, which will make that copy into an image you can burn in Disk Utility.
But since there's no CSS, region encoding, or anything else to get in the way--and since this is coming off of a DVD-R already--you should just be able to make an image in Disk Utility and burn that.
Good luck.