Just having a few minutes to stretch and breath is wonderful.
A great DVD for a beginners and intermediates is Power Yoga for Every Body.
http://www.amazon.com/exec/obidos/tg/detail/-/B0000A2ZR7/ref=pd_sim_dv_1/102-6261898-3971351?v=glance&s=dvdWhat is nice about this DVD is it has many different practices, all at beginner, intermediate or advanced level. So you choose the workout you want at the level you can manage. For instance, you might choose 45 minute strength practice, beginner level. Or 1/2 hour morning practice, advanced. It is a great DVD to start out with, and once you get into better shape, it will still be useful. I also think the instructor does a good job of describing the poses.
Another DVD that might be good for you is this one.
http://www.amazon.com/exec/obidos/tg/detail/-/B00062DKO0/ref=ord_cart_shr/102-6261898-3971351?%5Fencoding=UTF8&m=ATVPDKIKX0DER&v=glanceI haven't done it, but it sounds good and Rodney Yee is a hottie.
I will recommend that you take several classes from a certified instructor just to get your alignments right. If your finances are up to it, you can have an instructor come into your home. I go to the local Y where they offer child watch. I also have a punch pass for the local yoga studio. I go there when I can find someone to watch my kids.
One last hint, yoga practice is much more effective if you practice often. So it is better to do a short easy practice everyday, or nearly every day than it is to kill yourself twice a week. I set aside time every night after my youngest is in bed to practice for 20 minutes or so.
Good luck!