Ps - long distance running is as much about the mental side of things, as it is about your physical fitness.
That`s why long runs are so important - 15 miles plus, as not only do they help give you physical capability of completing a marathon, they also programme your brain, to accept being on your feet for hours.
When you get to the long run stage of your training, don`t worry too much about times, as we`re all different and run at different speeds. Find a speed and rhythm that`s comfortable for you and try to stick to it on your long runs.
Also, use training plans as a guideline, as a lot of them have been designed by high end athletes, for high end athletes and as a result aren`t suitable for your average runner.
One of the biggest mistakes I`ve made in the past, with organised events is failing to look at the gradients involved and getting stung badly as a result - it`s the first thing I look at now !
I think the Edinburgh marathon, has some pretty big hills / gradients in it, which will require you to put in some hill training - look up hill sprints / hill repeats.