This is not specifically about DDP yoga, but yoga in general.
I always find it cute when people say they are the "least flexible person" when starting yoga, because you don't have to be flexible to try yoga, you just have to TRY, modify the poses that you can't get into, and then one day you will get into them because yoga improves your flexibility!
The instructor on the DVD should typically have some cues to make sure you are in the poses correctly, but if you don't go to a class, just do a bunch of research on poses you have questions about.
Even after doing yoga for a year 4-5 times a week, I have TONS of questions. As I move through my practice, I get further into poses and then have even more questions. I do a lot of research though and different instructors give me different cues that facilitate the learning process for me.
If you can, going to an actual class will probably be helpful, but even better than that if you could afford even just a 1-hour personal session with an instructor it would help you. Don't know if that's available in your area.
Just be careful and don't do anything that hurts, and enjoy! I'm excited for you :-)