Sending in my Xbox 360 for repair?

im sending in my 360 to microsoft to get repaired (RRoD). does it matter if i send it throught the post office instead of UPS? also, does it matter what kind of box i send it in? I was going to use a the box that i bought a used original xbox in a while back, but would it matter? I was looking at the repair faq and it said something about not using the box your console came in?