Just looking on Amazon's website, it looks like that there's going to be a book that teaches you how to design a game for the X360. Unfortunately, it won't be out until late spring of next year. Looks fairly cool, tho:
http://www.amazon.com/Professional-XNA-Game-Programming-Nitschke/dp/0470126779/sr=1-1/qid=1166131339/ref=sr_1_1/002-4011097-0251206?ie=UTF8&s=books
http://www.amazon.com/Professional-XNA-Game-Programming-Nitschke/dp/0470126779/sr=1-1/qid=1166131339/ref=sr_1_1/002-4011097-0251206?ie=UTF8&s=books