I started from week 3 because I'm about 2 weeks fitter than a couch potato. Oh yeah, I'm ripped!
So I Google'ed around for blogs of people who have done the C25K program. None of them go beyond 4 weeks. I think, oh, one of them ended at Week 6. Not a good sign at all, I don't think. Well, here I am telling you. I am now on week 4, week 3 was too easy (I'm ripped!).