Books on tape have been around a long time, when I was younger we would sometimes get an audio book to listen to in the car on a long trip. Now that people carry mp3 players almost everywhere there is no reason to wait for a road trip to listen to a good book. And, like ebooks, there isn't the pressure to sell huge volumes that is inherent when publishing a printed book, so it is much easier to get into. In fact with just some audio recording software and a high quality microphone you can get started recording your first audio book.
Once you have decided to record an audio book you can start getting prepared. You want to be very familiar with the text. Read first and record second. You can do some editing of the audio after recording, but you want to keep that to a minimum and keep a flow to the prose. Being familiar with the text will help you keep a steady pace. Keep your pace in check, you don't want to zip through it fast so that the listener can really appreciate and hear everything you are reading. In addition to keeping that slow pace, be sure to add pauses after sentences and paragraphs, and beware being monotone. Try to breathe some life into your reading, no one will want to listen to you drone on in a flat voice. Another suggestion would be to consider printing out a hard copy of the book. Unbound, single-sided pages will make page turning easy.
Once you are prepared you just need to schedule yourself a chunk of quiet time to sit down and start recording. You can estimate the total amount of time you will need by timing how long it takes you to read through a single page and multiply by the number of pages. For a longer book you might want to break it out into more than one sitting. A good choice for audio recording is WavePad Sound Editor. By recording directly into an audio editor like WavePad you can easily go in to the recorded audio file when you are done recording to cut out any places you might have stumbled or make any other adjustment that might be needed like amplifying or equalizing the audio file or eliminating any background noise that might have crept in. And if you recorded in more than one session you can merge the files together before publishing your final mp3 file and sharing it with the world.