Hi!
I can't give you any precise numbers/amount of weight you could lose this way, because it also depends on each person, we won't all get the exact same results at the exact same moment. Now, something that you can do and that won't get lost is:
- Resistance training (lifting weights). Developing your muscles will also make them need more energy; of course you need to combine that with an eating program, but it helps in burning some more calories than just your average basal metabolism would need. Plus you'll anyway look great from the outside too

(No risk of becoming bulky, by the way.)
The thing with this is that you need to work your muscles to their full extent. I'd say that preferrably, you should aim for series of 10-15 reps maximum. If 15 reps with a certain load are too eays to do, it's time to up the weight load. If you can barely do 5 reps, then the weight is still too much. Normally you should feel when "enough is enough" - that's when you can't take one more rep anymore. Start easily at first though, especially with muscles that we don't use often (for instance, I personally have a hard time with biceps, as I've never really "used" them before, while my legs are stronger from carrying all the weight). It's best to up from something too easy, rather than start too hard and then injure a knee or elbow.
45 mins to 1 hour a day should be good for this; too long would cause more harm than good.
- Cardio-training: This is to actually burn the fat. You can do it on a bike, elliptical bike, treadmill, walking/running outside... You however need to do it during a significant amount of time each time, basically more than 45 minutes, else it's not useful. The reason why is that during the first 20 minutes, you'll essentially burn carbs (in the blood stream and stored in muscles - I'm not sure about the English name for this one, glycogen maybe?); between 20 and 40 minutes, you still burn the remaining carbs and start tapping into the fat stored in your body; after 40-45 minutes, you'll burn the fat. So less than that is still good for general health, but not for losing weight.
Also - there's a certain limit to reach, and one you shouldn't go past. There are formulas to compute this, the "simple" one goes basically: 220 - (your age) = your maximum heart rate. In order to lose weight, you need to perform your cardio exercises at at least 50-60% of this rate, and not more than 75-80%. As an example: I'm 25, so following this formula, my max rate is 195, and to do effective training, I must stay between 98 (50%) and 156 (80%). In the beginning, you'll probably go high in your own range, until your heart is trained enough, and will then pump a bit more slowly for the same intensity of exercise.
I'd say that ideally, you should alternate both during 6 days each week. Cardio-training tends to get lost if you don't do it too often, while muscle-training requires a day of rest (~48h) between two sessions (working your muscles to their full extent "tears" them a bit, so they need this time to "repair" themselves, which is what makes them get stronger in fact).
However, for workouts DVD, I'm not sure of what exactly they make you work. Probably cardio more than often, yet I don't know every DVD out there, so I wouldn't give my word on this. They're probably good though if you're just starting; some of them for instance make you work with small weights, which is better than nothing after all, and allow you to start training your arms in a soft way. Or you can try to get free weights and do that at home (not sure about the prices where you live, but in my town, I've been able to find starters' sets for like 20-25 $).
You'll sure feel more energized, in any case. And also beware the scales if you do weight-lifting - i.e. 2 pounds of muscle take less room than 2 pounds of fat, so after a while, you may see your scales not moving and think that you haven't lost anything, while in fact you've lost some fat (and in inches!) but gained in muscle. Regular scales just don't make the difference, and give you the total weight.
Phew, okay, that was quite long, sorry for the novel. I hope I haven't forgotten or misunderstood anything (nor used the wrong word, sometimes I get carried by my thoughts and use a word that is more French than English), but at least from what I've already read on these boards and from other sources, it should already take you somewhere regarding exercise.
PS - The time durations (45 mins etc) I've given are "ideally" to really help losing weight; if you feel you need to start with less, by all means, do it! I wasn't biking for 45 minutes straight on my first cardio workout either; everyone needs to get their body into shape again and progressively improve, and starting pumping out like an ox when you haven't exercised in ages is simply too much for a start. Remember that even 15 minutes "only" is always better for the health than nothing
I hope this could be of help, and good luck with starting again!
