There are a number of posts about this in the first page of this forum. I have done a lot of research as I am in the field for buying 2gb worth of ram for my rev d powerbook. Crucial originally had a different low power RAM chip out because the REV A and REV B powerbooks were not accepting the chips they produced. Which is most likely the reason why a lot of the current powerbook users are reporting that the RAM they purchased does not work in their current set up. I called Crucial tech support and they had very little to offer. They basically stated the Powerbook specific RAM was a lower power version. I asked if they have tested the cheaper version of that ram on the newer revisions of the current powerbook. He stated no.
I called a local tech store that offered both types of ram, and sell a large amount of powerbooks. They stated that the cheaper one should work in the new revisions of the al pb. Don't take my word on it. I am waiting for them to get an order before I drop the $200+.