Someone did try to sell me a book about multitasking for embedded systems and although it was dealling more with time critical multitasking where you have to garentee that some event will happen within some time period it was still very expensive at £80.00 for 120 pages in hardback concidering you can get most of the information from t'interweb anyway.Very nice if you want to write a fail safe controller for your local power station not much use otherwise.
I think most people sort of assume that if you start talking about operating systems and multitasking then you are talking about at least a 16 bit processor.