You cant just backup dvd movies with primo. Most movies are dual layered(dvd9) and wont fit onto a blank dvd media. To get it on one disc you will have to take out extras, foreign sound streams you wont use, and possibly even have to lower the video bitrate. Or you can keep everything and and put it on two discs.(much less time consuming) Check out the tutorials at
doom9.net to do either of the above processes.