Right now I'm about 25 lbs overweight, mid-30's, and I get really sore the day after jogging for about 20 min. I want to set milestones leading up to a half marathon. With a decent training program, is something like this realistic?

In 2 months: 5k (no walking)
In 3 months: 10k (no walking)
In 4 months: half marathon (maybe a little bit of walking, mostly running)

Also, does anyone have a training program that you'd recommend for a guy like me?