Most of the Kaplan material is exactly the same, with the MCAT books a bit more detailed but that won't hurt you. However I would recommend you get the Kaplan DAT blue book because there are several topics especially in biology that are covered on DAT not on MCAT, and vice versa. Also you may want to consider DAT Destroyer, DAT Achiever, and although I haven't tried it, Topscore.
The DAT overall is a much easier exam. I took my MCAT last August, and I started seriously studying for DAT's around mid January and took them this past Tuesday. I put in about 3 hours a day on average, sometimes I'd take a weekend off and occasionally I'd do an 8 hour marathon.
It wasn't too bad but I do have to admit the DAT is a lot more detail oriented. I got by doing well on the MCAT bio without knowing much detail, due to its passaged based nature. The DAT is all about knowing obscure details and being able to apply them...
good luck