Goodonya for doing the running! You only really need half an hour of cardio a day to keep fit and power walking will do the job, but actually running (jogging, whatever you want to call it) will get you fitter faster. The only concern I'd have is whether or not you've got good running shoes to protect your knees. I had to make a $120 investment in a pair of AirMax trainers to keep my knees intact.

I know running isn't everyone's cup of tea, but, for the purpose of motivation, I will mention that I've lost well over 30 lbs. in a single year of training and now have sufficient cardio and conditioning that I'm now prepared to run a 10k race and I'm looking ahead to training for a 1/2 marathon. Having been a butterball since childhood, this is an amazing accomplishment for me. The key is to find interesting places to run.