When I see really good instruction books, I smile.
Writing instructions on how to assembly a product is hard. Your audience is most likely coming at the situation "blind" with little experience, and there is little reason for them to invest time in becoming an expert in assembling the product because once it works, that knowledge becomes useless. Get it done and forget about it. Unless, of course, you plan on buying the same item again and again. With something like a bookcase, that isn't true.
Compare the typical furniture installation guide to what you get with furniture from Ikea. I don't think good instructions like this are an accident. I assume (can someone from Ikea confirm?) that they do usability studies: people with little experience are given the product and asked to install it as trained professionals watch them through a one-way mirror. The documentation is improved based on observations and interviews.
Now let's talk about the Apple Xserve installation process. I've installed, maybe, 6 Apple Xserve computers. The instructions frustrating. You continually keep saying to yourself, "Why would they want me to do that?" and yet, if you skip those steps you end up regretting it later, often having to start over from scratch. "Oh, now I understand. If you don't use your left elbow to support the frizenfrats, your right hand won't be free to slide the wingding into the snortplex." The design of the Apple Xserve is extremely elegant, but you don't realize it until you are done thus it is tempting to not follow the instructions precicely. If I went more than a month without installing an Xserve I would forget how to do it and feel like a newbie all over again. When you do it their way everything "just works." If only they could explain at the beginning what it would look like at the end. Word won't do justice to it. It's like explaining to a blind person what "red" looks like. I wish Apple would include a video showing how it looks and works when it's done. Demonstrate how it slides in and out of the rack so well. Then walk through the installation process, showing how the case is actually what gets attached to the rack, and the guts slide into the case. (If you've installed one of these things, you know what I mean.) After watching that, the user is no longer doing the installation "blind" and actual installation time would be dramatically reduced. Much less frustrating.
Sometimes the problem is simply fear of the unknown. People generally fear messing with the crazy, messy, wires in a home entertainment system. Consider the Tivo with its multitude connectors for video out: composite, HDMI, other acronyms I can't remember. They've put out a video that shows the installation process. I recommend people watch the video even if they don't own or plan on owning a Tivo. It's a good example of how to do a video introduction to a complicated process. The video is shot in a living-room, not a lab. Notice that the voice is friendly, plain-spoken (referring to "that cable guy"), even making commentary ("I love it when it's color coded") and using slang ("this little puppy"). It starts with an overriding premise: all connections will be "from out, to in" and this phrase is emphasized throughout. Watch it and understand.
Does your company make a product that would benefit from an installation video?