Here are answers to your questions, in order:
There's a DVD+R DL media and burner compatibility thread. Look through it to see if anyone else has had any luck with the drives you own. If neither are listed, check out VideoHelp's DVD writer section
. It has a list of DVD writers along with user ratings for general reliability of each drive. Choose the one that sounds better.
The general consensus in these boards is that Verbatim brand DVD media are the best. Considering the high cost of DVD+R DL media in general, I would go out of my way to obtain some Verbatim discs over locally-available brands to avoid making unnecessary coasters.
For burning software, I personally use Imgburn because it's both free and very feature-rich while being fast and small. It's slightly more complicated to use than CloneCD because you need to set layerbreak manually. If you don't think you can handle it, download a trial copy of CloneCD to do the dirty work for you. When making backups, don't forget to tell each program to change bitsetting to "DVD-ROM". This tricks the Xbox 360 into thinking that the disc is a printed DVD instead of a DVD+R DL.
Don't burn at a speed any higher than what your DVD writer and medium can support. DVD+R DL media is expensive, so start at 1X for your first backup and work your way up from there until you start making coasters.
Oh, and proof-read your posts before clicking "submit". More people will be inclined to help you if they don't have to work at deciphering your communiques.
EDIT: You *must* use DVD+R DL. DVD-R DL don't support bit-setting. I've heard that newer firmwares don't require backed up discs to be bit-set, but I'd play it safe and burn on DVD+R DL with proper bit-setting to ensure maximum compatibility.
Edited by qifanxi, 19 November 2006 - 07:30 PM.