One of the best things we ever did was pick up a used treadmill for $25. We discovered that we'd actually USE the thing! We also have a bowflex that now proudly sits next to the treadmill in our new addition--we have a section of the family room/tv room/Wii room set aside for exercise equipment.
Walking...definitely. I'm up to a full hour. Our treadmill (the new one that we bought last year) thankfully has one touch incline up to 10% and goes up to 10 mph so that when I get there, I can jog. I started at a 2% incline, and just 2-3 mph. Now (10 days later) I vary the incline from a minimum of 3% to 8% and speed varies from 2.4 to 3.0 mph. I go an hour per day, 5 days a week. I'm getting ready to start using the bowflex for part of that hour, 3 days a week too.
Start easy, but remember how hard you have to work to start, and keep that up. When it starts getting easy, beef up your speed or resistance so that you're still getting the heart rate up. Wear good, well-fitting shoes, stretch your feet if you need to! I've always been active, just got fat. So I started with a lot of walking ability. You have to do what works for you. Stretch yourself a bit, and one tip to starting is intervals. Walk at a speed that makes you huff and puff a bit for a few minutes, then slow it down for a few minutes. You'll be able to go for longer times especially when you're first starting out.
Resistance bands are a cheap way to get strength training in and can be used while sitting or standing. I also have a couple of the big exercise balls with a dvd for their use. Yoga is awesome, I have a couple of basic Yoga dvd's made my Living Earth.
I'm 41 and this is it for me--this is my time to make my body the best I can make it! You can too!