If you want to get into some fat-burning, I'd recommend interval training, where you walk and run alternately. It keeps your heart rate up to fat-burning levels without wiping you out!! I've been doing this for the last 6 weeks and it's working well.
Walk 5 mins (to warm up) at a brisk 3.5-4 mph; then run at 5.5-6.5 mph for 60 seconds, then slow to the brisk walk for 90 seconds. Repeat the 'walk and run' intervals six or eight times, then walk to cool down for 5 mins. Do about 30 mins in total at least, but 60 mins would be better!
Three times a week is good, with weight training, swimming, biking etc in between - something which doesn't impact your knees.
As you improve, you can up the running time, and gradually get up to running for five minutes, walking for 3, or however you feel comfortable.
Cool Running :: The Couch-to-5K Running Plan has a good system on the website, you can start the training prog. and just stop at a level where you feel good.
There is a really useful podcast of it at
Podcasts so you can run/walk to the instructions and music on your ipod.
Put the incline on 0.5 - 1 if you like, but it's not vital. When walking you could up the incline, for a bit of variety.
have fun!
