If you want to run (or walk or jog) a marathon you can. It takes hard work and determination but you can do it. As Kim recommended, get a good pair of running shoes at a good running store. After that I would start training for a 5K, then a 10K, then a half, and then a full. There are plenty of programs out there. A PP mentioned the C25K program which is a good start. After that I would go to Hal Higdon's
website and pick a half program, then a full program.
The key is to start slow and build up at a reasonable rate. I would stick to the 10% rule until you are a more seasoned runner. The rule says you shouldn't increase either the distance of you longest run or the total mileage per week by more then 10%. This is fairly conservative but will keep you from making the mistake many rookie runners make and double your mileage in a week.
As for the schedule problems, make you runs an appointment on your calendar. If they are inked into a spot and you treat it like an appointment instead of an option you will be more likely to get the run (or walk or jog) in. After a little while you will find a way to get them in. There are days I don't even go out to start my run before midnight in the summer but I make sure to get the runs in.
Good luck, you can do it. It is a rough road but once you put in all the time and effort training you will understand why the 26.2 on race day really is the easy part.