I can offer perhaps a little bit of info on the subject. My friend's son James has Asperger's. As I understand, they are all different (age may make a big difference too, James is 8), but maybe some of this will help. I don't think I will be very organized as I am thinking and typing at the same time, but here goes:
James' sensory perception is very extreme, so extra noise, extra touch, anything can cause his mind to "disengage". In light of that, I would probably not try to use CD's with him until he was very comfortable with me and we were well into lessons. I would try to keep my mannerisms (sp) very simple, not throwing around the number of books I usually do--charts on my lap, arm motions, etc. Perhaps One book at a time, using a very calm voice and slow movements. The boy I know is very sensitive to touch/space also, so I would be very aware of physical space issues and sit where he feels in control of the "space" around him--not boxed in with a teacher leaning over him. The boy I know is very intelligent, but he deals with this "sensory" problem. When overstimulated, he has a hard time winding down and focussing--sometimes even has a breakdown where he goes into a corner. So, I wouldn't do a typical ADHD regimen of switching activities every few minutes from piano to floor games, etc. For him, this could be "too many changes" which he is definitely not fond of. I WOULD use a very strict schedule. For example, always start with a game, then flashcards, then do a warm-up, then do Lesson Book, .... The boy I know, when given a challenge to win something or get a reward will be very diligent so I might incorporate short goals during the lesson "let's see if you can sit totally quiet for 2 minutes while I talk" "let's see if you can play the same melody in left hand and right hand" "let's see if you can do them in opposite directions (contrary motion excercises). These kinds of "I bet you can"s can really **** him in. As I mentioned earlier, the intelligence isn't a factor (at least for James), so I wouldn't worry about making something "easier," I would just try to limit the distractions.
Normally PA is my first choice, but with James, I might go a different route. I would pick a lesson book that doesn't have too much writing all over it (if possible) that is still pedagogically sound (Hal leonard (which I use) and Noona Comprehensive come to mind as looking very simple yet interesting to the student (I haven't used Noona yet with a student.) Any fun stickers/highlighters might be incentive to keep attention (these don't seem to distract as they aren't words, noise, etc.). Last, I probably woudn't send him home with work from 4 different books to do. As it may be overwhelming. With James--who can't focus to want to write much--I might actually just skip the theory book and try to do that orally. Then do technique by rote, and only have a Lesson & Performance/Recital book.
Again, this is just my opinion based on observations of James coupled with the mom's comments on his behavior at home and at school. I'll see if I can have his mom read this and see if she might add anything to (or delete :-) ) my suggestions. I read some of the threads on this over at Yahoo, and it also sounds like each child is very distinct. It may take a while to find your way. Good Luck, and let us know how it goes!