To a point you can. Some people learn very well from just watching, but for some people movements need to be broken down for them. A video can only do so much. If you aren't "getting" a move there is no one to show you a different way to approach it that will help you better understand. There is no one to work with you.
How to videos have their place and can be a terrific resource. I have many Belly Dance DVDs and I have learned something form all of them... some more than others. I like the instructional DVD as a supplemental source of education. They are awesome when you are needing more information on a special topic such as prop work with a veil or sword. As far as the very, very beginners instructional DVD goes, well, I am not convinced.
If you are interested in trying Belly Dance, I urge you to find a local Instructor. If you are intimidated by going to a class, don't be! A beginning Belly Dance class is full of other Women trying something fun and new and will be too busy trying to catch on to those figure 8's to be judging you! If you are sure you would rather just move around a little in your living room, I say give it try. Belly Dancing to a DVD is better than NOT Belly Dancing at all :-) Although, expect to get to a point where you feel stuck and not sure where to go... and that's the time to finally get over it and join your local beginning Belly Dance class!