I've seen the movies. I know that Dooku cut off Anakin's hand during Episode 2. However, I'm in the process of reading Dark Force Rising, and in it, Mara Jade tells Luke Skywalker that Vader lost his right hand as a result of the Emperor's anger over losing the first Death Star.
So, which is it? Clearly, I'd assume the book is in "error" here. But, is there something more to this?