Do I get the same amount of exercise for running 3kilometers in 25 minutes and walking 3 kilometers for an hour?

Essentially. Depends on your goal. You'll burn about the same number of calories. If you are trying to build cardiovascular stamina, running or intervals of running and walking are more effective.
Yes, sort of. Walking versus running the same distance will burn the same number of calories. However, running tends to be more stressful to the exerciser's system than walking. Therefore, your metabolic rate will remain elevated longer after a run, as opposed to walking. Therefore, running burns calories than walking when you consider the extra burn.