Theres no such thing as a DVD+RW DL. There was talk of re-writeable Dual Layers but they never became available to the mass market.
Those of you eager to play this game I recommend just buying it. Theres no point in going out and buying a new burner and media for this one game. Unless Ninty start doing this with all their first party titles (unlikely) then you'd be spending as much to burn the game as you would to just buy it retail, maybe more actually.
People with flashed 360's will already have a DL burner, so sure, go for it, but the rest of you without I'd really think about just buying the game.
Show some support for a change. Just my 2 pennys.