Music Law book? Is that a passive-aggressive incentive? Will we close the sale by answering? (Or perhaps if we do answer, will you be less likely to buy?)
Right, you had two questions. It is infringement to copy audio samples from B-movies. Taking a few seconds may qualify as a fair use -- though keep in mind that at least one court has (perhaps illogically) held that taking any audio sample (regardless of its size) violates the sound recording copyright. You're okay to use the samples if the film is in the public domain. (Note, even in public domain films, composers have claimed separate musical copyright.) You may be able to defend your activities depending on the fair use factors. But as we always point out, you can only "win" a fair use argument if you're prepared to fight it in court. Considering the vast amount of unchecked sampling, we think the bigger issue is whether the owner of the B-movie rights will ever learn of your use, or will care if they find it.
Using the movie picture on a t-shirt. If you edited the image you can stop others from using your modifications. But you don't "own" the image. You only own what you added. The owner of the underlying copyright can still stop your derivative use. We don't know if you would get it trouble for using the image -- BTW, it wouldn't make any difference whether you sold them or gave them away for free. Again, that's a matter of anticipating the likelihood that the film's copyright owner would spot your use and care. Our guess is that you'll fly below the radar. (We answered a related question in a previous entry.)