I'm in the minority here, but I think in most cases for NEW students in BJJ, Boxing etc., DVD's are a BAD idea. DVD's in most cases require training partners, and often times are way too advanced for the beginner. The foundation of your sport whether BJJ, Boxing etc., will suffer because you won't really learn how to build it, because DVD's won't explain things in enough detail and stress this importance enough. BASICS and FUNDAMENTALS are everything in combat sports. If you have a WEAK foundation, you can only take your game so far! Now guys like Rich Franklin or Eddie Chambers learned a lot from books, DVD's etc from the start, but that's RARE, and to get to the next level they got personal coaching.
A FAR better idea is go to a local fight card or grappling tournament, and see which school or gym WINS consistently, amateur stuff is even better to watch because it will show NEWER guys, and a lot of the amateur coaches are better at developing the basics, than somebody who only works with POLISHED professionals, plus it gives you more guys you can spar against with similar skill levels. If you see a gym have a bunch of losses, (NAGA tournaments, USA Boxing events etc.) then more than likely the coaches aren't that good. From there you will have a better idea where to train. The teaching ability of coaches varies widely, as it would in other things like PICKUP. A lot of guys call themselves a coach, but are really just HACKS, or ex fighters who learned the WRONG way from the start, which is why they weren't very good, and thus teach you their shitty style. Get with a good gym-school, you might get your ass handed to you a few times, but that's what makes you better. DVD's also don't address CONDITIONING, or MENTAL TOUGHNESS the way a GOOD coach would, something you really can't develop unless you get put through FIRE in sparring etc. You would also be surprised how many coaches will work with you for very little $, simply because they have a PASSION for the game.
Now for more advanced guys DVD's may help, as new moves can be added to your arsenal, but you already have the BASICS and a good foundation down, because your advanced.