Just go out an run at first to see what you're capable of. Run a measured distance of some sort and use a stopwatch to see how long it takes you to complete. This way you can see if you enjoy it or if it bothers your joints at all. Once you figure out the basics like that, start up a set plan. With a combination of eating right and running daily, I was able to lose all of my excess body fat and feel great over the course of 2 months.
During lunch time, I can comfortably squeeze in 2-3 miles before I run out of time. Sometimes it bothers my knee or ankle, so I don't like to push it any more.
Go to a running store and get fitting for a good pair of shoes if you're serious about it, you can also pick up a copy of the latest Runner's World mag while you're there. It's got a ton of good info, as does their website if you don't like paper.