I just started the C25K program a few weeks ago. We are on week 3, workout 2. My best advice is to work your way up to it. I had stopped walking for several months and when I started back my feet and shins were sore. We decided to do brisk walking for 1.5-2 miles a few times per week for a couple weeks before starting the program.
Just like the site says, go by time and not by distance. My friend jogs much faster than I do and there is no way I can keep up with her distance, but we are both running 3 minutes, so it equals out.
If you need to repeat workouts it's totally ok! Just be proud that you're doing the time!
There is also an amazing app for C25K. Mine is from active.com, but there are several. It will track your time and fade your music out to tell you when to start jogging or walking & many more things! I LOVE this because it was a nightmare to try to read my watch or cell phone while jogging haha!
Best of luck to you! I know you'll do great!