Hmmm, I don't believe the books. Mainly because every person is different and has different needs. Now, having said that, I think it's great to get some opinions of what has worked for other people. Whether it is from books, talking to other people at the playground or posting to this site... it's great to learn from other's experiences because you may find some advice that you wouldn't have thought of. I suggest you read a few articles (I like Parent's magazine). I imagine you can get some info online and the library, rather than spend money on one book. I bought a few discipline books before I realized each author has their own opinion and not all are the right answers for me and my kids.
Now, the actual problem... whether to train or not. My daughter just switched to underwear at 33 months and she's doing great. She has occasional accidents, usually because she's caught up in something (playing outside or visiting someone and playing with a bunch of new toys). Her sister switched to diapers at 33 months too and did great. Here's what we did...
1. Put a little potty in your bathroom. When I would go to the bathroom, she would follow me in and talk to me or bring me things. So, I would say, do you want to sit on your potty while Mommy sits on hers? At first she'd do it in her clothes and with the lid down which we didn't discuss much.
2. When she needs a diaper change, we would do it in the bathroom. We used pull-up diapers and talked about how they were big kid diapers and how they pull up just like underwear.
3. When she has a bowel movement, dump the poop in the potty and let her flush it. Say things like, big kids poops in the potty so we can flush it away and not have to smell it. Do you want to be the one to flush your poop? She eventually would insist that we put the poop in the toilet. Then I would say, ok, now you poop on your potty. She was so regular that I would know what time of day she would be most likely to be successful.
4. Start discussing underwear and how cool it is to be a big kid and get to pick out your own underwear. Talk about some of the cool things you can have on your undewear and how fun it will be to get some when your ready to use the potty.
5. Once they are successful in the potty and able to keep their diapers fairly dry, you're ready to let them switch.
It sounds like a lot more than 3 days but really you're just conditioning them while they are still in diapers and not really ready for the underwear. Also, it's very important to dress them in clothes they can handle on their own. If you are really ready to do it, you can let them just run around in their underwear for a few days till they learn.
We're in the process of trying to switch from the little potty to the big one. It requires her to get there a little earlier since it takes some time and effort to set up the step stool and potty seat.
I wish you the best luck and hope this helps. I hope you read a few potty training methods before you start so you can see what works best for your son. I wouldn't let age determine when you train, base it on your son's response.
Liz
p.s. My friend had only a few days to train her daughter (requirement for preschool) so she let her run around in just a shirt for 2-3 days. She hated the feeling of pee on her legs so she was forced to learn to use the potty fast. Since there were no clothes to soil (naked from the waist down) my friend only had to clean up the floors. It worked for her, but she was under high stress to make the cut off.