Who knew there were so many of us? I just discovered this thread. There are many responses -- more than I could read -- so forgive me if I repeat:
First, I love the Hal Higdon plans and have admired him since my teens, when I went to school with his kids. I was not a runner then.
Second, I also lost about 30 pounds slowly over the course of a few years through running/walking. I found that my running got faster and better every time I broke a plateau and lost another 5 pounds. To lose weight, the South Beach Diet was what I had the most success on, and the lean protein in it helped me to build muscle. I still tend to walk about 1/4 of the time in my normal 3-mile runs, with a little less walking if I'm in a race.
Third, I highly recommend racing, and if you can do a 5K, you can try an 8K next, such as the one in Hal's and my hometown of Michigan City, Ind. It's called the Tower Run. But beware -- most of it is on beach sand and it will take you a while. But it's fun and interesting.
Fourth -- I just did my first marathon team relay in the Baltimore Marathon, which was exhilarating. My part was 6.1 miles, which was no harder than the 8K (5 miles) I did in Michigan City on sand. There was something so emotionally gratifying about being part of a team, being relied upon by the team, and getting encouragement along the way from the city residents whose neighborhoods we ran through. It was the longest I had ever run. I did walk some of it now and then, but my team was fine with that.