The 'broken 5K' is deceptively simple - run 12 quarter mile intervals at around 5K pace, with 20-30 second recoveries. That is a very short recovery time; just enough time to slow up to a walk, take a few breaths and then start running again. I do my broken 5K workouts on the local greenway, which is marked out with quarter mile markers. It is not flat, but that makes it more interesting than a track. I find this is a great workout for all distances.
A friend of mine (Mark E) took this workout to its logical conclusion and did the broken 5K on a 5K course. That gave him a very good preview of the course, as he was running it at race pace.