Get a DENTPIN now. Its free and takes bout a few days to week to receive. You can sign up for the DAT now if you want, but its kind of foolish to do it so early.
Because:
A. you havent started studying yet and you're not sure when you'll finish
B. Its such a long time from now that if you want to change your date later you will have to pay another $25
C. There are enough test centers and days to take the exam that there is no difference or advantage by signing up today vs. April 2012 or even May.
After you get your DENTPIN, you can sign up to get approval for the DAT (that takes almost a week as well) and then you pick your Appointment Date (test date) you can sign up to get DAT approval and then wait to pick an appointment date later, but I believe it might expire after some time and you might waste that $320.
I say wait until next year to do the process. There is no advantage or real reason to do it now, plus if you change your mind about the date later you'll have to shell out $25 later. The test is given nearly every day of every week and there are enough times and centers to get whatever you want. Even if you signed up in June 2012. Good luck 🙂