I haven't heard of that book but I have been doing a pregnancy workout video called Fit Mama! It has 3 parts: a salsa session, a fat burning yoga session, and a floor session. You can break up the excercises 3-4 times a week and it's supposed to help strengthen the back, abdominal, pelvis, and leg areas for birth as well. It even has 3 different levels of activity for first, second and third trimester. It's pretty good and a lot of fun but expect to be a tad sore the first couple times. Not too strenuous.
Walking is great too but I felt I needed a little more fun and area focused fitness during this time. I highly reccommend this workout video.
EDD 01/12/04 With #1 baby - Joshua James!