i would encourage you to 'try before you buy' if possible at all -- check yourl local library system and hopefully you can check them out there.
I have had the QuickFix yoga/pilates DVD and LOVED it -- i wore it out literally. however, there is assumption in their instruction that you are familiar with basic yoga, so if you are completely new this may not be the best first one. I find Denise Austin very easy to understand in her instructions, but a bit chatty.
by chance do you have "Exercise on Demand" channel? there is a few basic yoga segments right now available. Also, if you have FitTV you may be able to record some yoga shows to try.
i first learned yoga at a class at the Y; so i may not be the best source for someone completely new to the practice. Enjoy it! remember it may take a few weeks to feel like you have your mojo on........don't give up!