From the "complete guide and Faq" for making backups thread, second one from the top. There are many other answers in there as well. I suggest you check it out.
"Now, you have an xISO. This is the last process! This is the easiest part too! Just open Nero, Alcohol 120, or DVD Decrypter. If you're using Nero, then close the startup wizard, and go to open, and use the drop down list and choose (iso, bin, cue) Do the same for Alcohol 120. Now, choose the xISO you just made. Now, for your settings. Make sure that you finalize the disc you're about to burn the xISO to. Make sure that you burn it at the lowest rate possible (4x is fine. If you can burn at 1-2x, that's perfect.) Now, with that done, press "Burn", and while it's burning, chill out for a while. It's going to take a good 10-13 minutes (for the average game). Go grab yourself something to drink or get a sandwhich. When you get back, it should be done. And that's it! Go play with your xbox!
For DVD Decrypter, Go to Mode>Iso>Write. Now choose where the ISO is, and set the burning speed as low as possible. Then burn it :)"
