I started running using C25k. I had to redo many weeks of it before I could run with any sort of speed at all. the key to the program is consistency because it all builds on itself. after C25k, I did bridge to10k, which works in the same fashion but is just longer times and distances.
When I first started running, I couldn't run for 30 seconds without being totally winded and feeling like I was going to pass out. Now, I'm running for close to 75 minutes without stopping. A BIIIIIG!!! part of that was getting past that mental block that would stop me every time. Even now, when I run, I can expect blocks at 10 minutes, 30 minutes, and 60 minutes. They aren't because my body is in pain and can't take it anymore, but because my brain tells me that i've had enough. I repeat to myself "The strong get stronger" and flick to a motivating song on my ipod and push through it. It isn't easy, but it is worth it. If you choose to listen to your brain and stop every time you want, your improvements will be minimal.
I use a marathoner from my area who has been coaching people for more than 30 years. He's awesome, understanding and has become a grandfather figure for me (he's 65 and is running ultra marathons!). There are plenty of coaching programs online - both paid and free, but I liked the accountability of having an actual person in my area. I would suggest completing C25k before you entertain any other moves. I started running in July 2010 at approximately 215 lbs. I ran my first 5k in September at 185 and am now training for a half marathon at 155-ish.
Bottom line: you CAN do this.
