Belly dance DVDs are a very good tool to help belly dancers to learn new moves, get new ideas or inspiration. It is possible to learn a lot from a good belly dance DVD, but if you are a total beginner, it is better to always attend some lessons with a teacher. The reason being that you can interact with a dance teacher and she can correct you if she thinks you are not performing your belly dance moves right, or if your posture is not correct.
It is difficult to judge these things by yourself, when you have no previous experience of a particular type of dance, and bellydance is not an exception.
However, good belly dance DVDs are very useful tools for deepening a dancer