if you got an iPod I would say that would be the way to go... But, the format will only work with the iPod. If that is not a problem for you, go for it. but if you want to listen to it on an mp3 player, do it in mp3 format. mp3 will work with the iPod too..
As for the books on tape, if you have a whole bunch of them and a bit of time on your hands, you can convert them to mp3 format with a good mp3 recording capable software for your computer. Music Match Jukebox will let you do this, altho MMJ is a very bloated and sometimes pain in the rear software package to use. basically you will hook your tape player into the input on your computer's sound card and record it. This will make it into a HUGE mp3 file. take that file and use an mp3 editor to break it down into smaller "chapters".
If you don't have the time, your best bet would be to replace them with the newer mp3 versions as time and money allow.