With DVD Decrypter, it's pretty easy. All you have to do is first crack the regional encoding, then go to the Mode setting on top. Then go to the ISO file and click "Read." If you want to rename the file or place it somewhere else, click the little folder icon. Then just push the icon on the bottom with the DVD to Hardrive icon.

.ISO File. Then to burn the file, all you have to do is change the 'Read' setting to 'Write' and follow the prompts in the boxes.

But, as most commercial DVDs are bigger than the single layer disks, it's not particuarly helpful. -_-O