LadyTaty, I meant to answer this sooner--I hope you're still on track to start C25K today! I was worried about my joints when I started (I was well over 250 and had never successfully run in my life). I started with walking, and walked for a couple of months before I started the program. I also read somewhere that if I was able to run slower, it meant I was running too fast! That surprised the heck out of me, but I took it to heart, and made my "runs" as slow as I could. I built muscle and endurance, and yesterday, I ran 3.5 miles--and I could have gone farther! It is astonishing to me that at the end of May I was trying to figure out how to handle those 60- and 90-second intervals, and now I can just lace up and go. But I am convinced that the reason I'm here--and here without so much as a shin splint--is that I put staying uninjured at the top of my list. I knew (and still know) that if I got injured badly enough that I got off-track for more than a day or two, I risked never getting back on track again. Patience is not my strong suit, but I've been trying to build that slowly, along with my muscles.
I didn't have to repeat any days or weeks, but I know plenty of people who have, and who don't regret it at all. Listen to your body, and push yourself a bit (but not too much!) in the early days, and it will start paying off for you before you know it.
If I can do it, anyone can do it. Good luck to you, and to everyone else who's just getting started.