Good luck with the running - I am a total running convert having taken it up in January 2008 at about 18st! I started by walking fast between lampposts and the bit by bit, I started jogging between lampposts, then I managed jogging between 2 lampposts.... by September of that year, I ran a half marathon! So, if I can run - anyone can!
I've kept running even through a pregnancy and gaining back up to 16 1/2 stone...just tootling around a couple of miles or so. I've found that it's never been as hard again to get back running - now I've lost a fair bit again, my running has a new lease of life. It makes you feel great! So, keep going, you're doing exactly the right thing using C25k and you will be amazed at how quickly your fitness improves. One bit of advice I would give is that as soon as you start doing more than 5 minutes of jogging or so, you really should get some running trainers - this is vital in preventing injury. Get yourself to a running shop where they will do a gait analysis and show you the specific type of shoe you need. You can wear any old thirst and leggings but investing in the right trainers is a must.
Have fun running!