I was using that couch to 5k app on the phone or the podcasts (just google it) and I found it builds the running up really well. It starts you off slow and once you get to level 4 and up it gets challenging.
I used to get a few injuries from running before, I got some running tips from a guy in a running club near me and I found out a lot i was doing wrong. Now I can run 3-5 times a week @ 30min session and only feel burn and lack of cardivasicular fitness.
Things like landing on my heels, landing with the legs in front and too long a stride make a big difference.
As for diet. I hear a lot of things I've never got any to work... I also have a friend who has some results because he cut artificial sugar out of everything....
But I do know a friend who does have very little body fat... He's a veg... a pure veg, no fish or eggs. I might try going veg for after crimbo and see if it helps cut the fat.