This thread is where a lot of the folks who are doing C25K hang out. You'll find plenty of encouragement there!
I just graduated C25K yesterday...and I can assure you that if I can do it, anyone can do it! You'll really be surprised at how your body adapts and those weeks that seem ridiculously un-doable become just another step in your progress.
When I started, I couldn't even run for 60 seconds. In fact, the first day, I only completed 15 minutes instead of 20 because I was afraid I was going to die before I could make it home!
For my graduation day run, I did a 5K race. A race with lots and lots of scarey hills. Not only did I finish, but I came in 23 of 40 in my age group!
I really can't say enough about how amazing the C25K program is. It changed my life!
And to answer your other question, I am NOT a skinny running chick! I'm 5'6" and hanging out between 221# and 224# (I really need to get the scale unstuck!).