I don't know what it was, perhaps the novelty of using my new geek toy (my ipod touch) but this little $4 or $5 app did the trick to push me to add jogging to my workout and step things up beyond just walking. When I started the fitness challenge last fall, I was doing walking workouts and it was enough to help me start dropping some pounds. Shortly I was finding that I could walk for a half hour to an hour but was not really coming home good and sweaty. A friend of mine started posting on facebook that she had completed her "couch 2 5K" workout for the day and I was intrigued. I had (and still have) NO PLANS to ever run a 5K race, but when my husband gave me an itouch last year around Mother's Day, I looked into the app again. It turned out to be the first one I downloaded that was not free. I feel like I have definitely gotten my money's worth out of it and was ecstatic when I finally made it to the last workout and was able to run for 30 minutes straight without stopping to walk. I may even get the 10K program on my itouch sometime to help push me to the next level and hopefully increase my stamina a bit more.
Here is a link to explain a little more of what this program does. You could use a stop watch and time yourself the changes from walking to running, but the app does that for you and cuts into your music to tell you when to switch from walk to run and even notifies you when you are half way done your workout.