If the dvd is not commercially made, and therefore has no encryption, you can do a simple copy using ImgBurn.
ImgBurn is a free burning program, found here: www.imgburn.com
Start ImgBurn and click on [I]Create image file from disc[/I]. What you are doing here is making an ISO file of the entire disk you want to copy. The ISO file is saved to the hard drive, and once there you can start ImgBurn again and click [I]Write image file to disc[/I]. Import the ISO file you just made, set your burn to a moderate speed (8x usually works for desktop burners) and use good quality disks, like Verbatim.
This process should work for any non-encrypted disk that you have.