Biking will definitely help you to lose weight--it burns calories, and burning calories is the point. It doesn't matter where you store your fat or whether you run, walk briskly, cycle, swim or do tae-bo. You want to get your heart rate up and KEEP it up in order to burn calories. Some activities burn more calories than others, but ANYTHING is a good start.
I'd recommend 30-60 mins of cardio a day, depending on your level of fitness. And push the intensity: walk QUICKLY with your dog so that you're slightly out of breath. You want to push yourself as much as you can but without pushing so hard that you hurt yourself.
Running is tough to start. Lots and lots of people have found success with the Couch-to-5k program. It starts you with intervals: a minute of running and a few minutes of walking and gradually increases the running time. Check it out if you're interested in running:
http://www.coolrunning.com/engine/2/2_3/181.shtml
The worst thing you can do is decide, 'I'm going to take up running' and then start sprinting down the street. It's a recipe for injury and disenchantment.
(I've done it many times, always hurt myself, decided that running isn't for me, and went back to the couch and the chips! Not helpful.
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Good Luck!