Start with intervals, and start SLOW. Work your way up. If you are on a treadmill, I'd do my jog/run intervals at 5.0. When you first start, walk for longer than you run: 3 min walk 1 min run repeat for 20-30 min. (or however long you can last) Even if you feel like you can keep going after the minute only do the minute because it gets harder later in your work out. The next week do 2 min 30 sec walk, 1 min 30 sec run, repeat. Each week reduce your walking time and increase your running time. The short intervals are a good starting point, after a week or 2 if you are feeling like you can do more, give it a try and see how you feel... you might be pleasantly surprised!
As far as breathing, for me its a funny balance. Definitely a regular, rhythmic breathing pattern is important for me to last, but if I focus on it too much and try to do something unnatural it just makes it worse.
Often after a few minutes of running, even when I've started with walking, I find that my body is finally warmed up and its not so bad. For those first few minutes, it usually sucks, though.
The couch to 5k program online is a good one for a beginning runner. Check it out.
