I see that this topic has gone on for some time, and would like to add my 2 cents.
OK... for all of you who think that you CANT use CD-R.. You are all WRONG!!
You can use CD-R and you will find that if you DONT burn at the full speed of your burner (%50 works fine every time for me), MOST XBOX's will read them.
As for the percentage rate of games that will fit on CD-R, well that has risen aswell due to 800meg CD-R and the use of Quix and the Avalaunch dash.
I use UnleashX my self but boot to Avalaunch for ISO creation, uploading using Qwix.
For those of you who dont know, Qwix incorperates a cross link file scanner.
This finds duplicate files that are some times written to the game disc to make it larger than a standard 4.7 gig DVD (meaning you cant it up as we only have 4.7 gig blanks ATM) and removes them when creating an ISO.
In 1 case, I found that a game was 4.9GB, used Qwix to create an ISO and removed the cross linked files and then became small enough to fit on CD-R.
I further looked at the games folders and found that they had place the audio/video clips repeated 5 times in 5 diff folders. Sneaky ay???
Try them both for your self and you might find that you will save some cash on DVD's!!!
Ok.. another alternative is to get ISO Craxion and burn multiple games to one DVD and use the menu maker incorperated.