I'm going to second DrNotherner. I found Couch to 5K because of Mumsnet. If you keep it up, you will be amazed when you look back from where you've come - I'm now doing a 10k programme and just ran 7 miles today. 7 miles! Get me - this is someone who doesn't run.
When I first started the Couch to 5K, I found the 90 second runs such a struggle, it was awful. I had to push myself to finish and couldn't see a future. I'm still pushing myself sometimes, but...many times I find myself running and smiling - I'm moving, faster than walking, and my body is keeping up with my mind. I'm not a glamorous, sporty, fit runner (read sweating, shuffling, red-faced runner) but that makes it even more important to me. I'm moving, more than just 90 seconds each time now, I'm running for 9 minutes segments, for repeats of more than an hour at a time. I never, never thought I could do that.
It's made me realise I'm stronger and more determined than I thought.
This running thing teaches you more than just running! Keep it up - and if you pause, and think you've failed, you haven't, you can still just start it again and take it gently. That's the beauty of Couch to 5K. You don't have to be an athlete, but it can teach you how you can gradually, slowly, become something you thought you couldn't.
Good luck, and enjoy it!