Good luck I was in the same boat. I had never ran until May this year, and was overweight by quite a bit. Do couch to 5k just repeat weeks if they are a struggle, then when you can do 5k find a half marathon plan you like. I use asics.co.uk you can make it as many weeks as you want and start at the level of able to run 20 minutes or so. So get to 5k then ASAP start on a half marsthon plan and just accept you will have some bad and some good weeks, just keep plodding along and you will be fine.
It's also great for helping to tone your body.
Just don't be afraid, plod along at your own speed, and don't do things for others do it for yourself, I am so proud that I can run a bit now. It's a great feeling.
Edited: 25/08/2012 at 18:48