You don't need to "power walk" to lose weight- I just walk briskly for 3 miles most every morning, and by doing that alone I have s-l-o-w-l-y lost 20 pounds over 11 months without dieting. That's about 1.6 pounds per months. Could have lost more with cutting back food, but am happy with my acheivements so far. Actually, those 11 months went by very fast and now I feel like i'm "suddenly" 20 pounds lighter. Great feeling.
Now I have added biking to the mix, and my weight loss is happening a bit faster (haven't given up my walking though).
My best advice to you is to keep your bike rides FUN so that you do them more often. Don't make them into a drudgery that you'll start avoiding. Start SMALL with easy goals! When you acheive them, you'll naturally want to do more bit by bit. Remember, this is NOT like some crash diet. It's a lifestyle change, so take your time and make it enjoyable. If you love doing it, you'll do it more!
First, congratulate yourself on your great new attitude. Then, reward yourself with a little spin around the block or down to the store. Make it part of your life. Buy yourself a "lucky shirt" or a nice pair of walking shoes.
You ROCK, girl!!