http://www.amazon.co.uk/exec/obidos/ASIN/184310850X/ref=ox_ya_oh_productWe recently bought this book for my youngest son to help him understand his brother's Asperger's. Whilst it doesn't focus throughout the book on what Asperger's is it is a remarkably good resource for siblings. It goes through all the emotions that might be associated with having an Apserger's sibling such as being angry at them, frustrated, protective, confident after seeing what their sibling has to contend with and the one I think we all get - being puzzled! It basically lets the sibling know that it's ok to have both good and negative feelings and it can be used to help start talking about it all.
It's written from the point of view of an eight year old boy who's older brother (2 years older) has Aspergers. It briefly talks about what Asperger's is like for his brother (describing some of the behaviours) and then goes through the feelings. Each feeling is under it's own header so it is easy to find if you just want to talk about that one. There is appropriate use of humour and simple line drawing illustrations. I have read some to my youngest and he picked out some of the poitns straight away and began to talk about them. I would say it is a really useful resource for siblings buit also for parents. It looks at Asperger's from a different point of view to normal and I found this fresh point of view helped me to think about how both of my children are affected by Aspergers and how I could help both of them, even though only one has it.
I hope this was helpful, I'm happy to answer any questions about the book.