You will find a stack of info on this in the stickys located at the start of this forum.
Basically. your pc won't read an xbox disc. You need to connect your xbox via it's network port located at the back of the box, to your pc via it's network card. Then, using a utility like flashfxp loaded on your pc, you can access your xbox and, with the game in your box's dvd drive, copy the files from the disc to a folder on your pc hard drive.
When you have done that, you can either make an iso of the game folder on your pc (method preferred by me) or use the data burn method (preferred by others on this forum) and then burn to a blank dvd disc using Alcohol 120%, recordnow max or other burning program (preferrably not nero though).
Check out
www.xbox-scene.com for some great tutorials or pm me your details and i'll send you a tutorial on how I do it.
Hope this helps.