just do rollouts: http://www.youtube.com/watch?v=c0nJWHb6WZU
They hammer all the muscles around your midsection, you won't need anything else. Don't get me wrong, core work (planks, pallofs etc) is good, but rollouts count as core work that is also challenging enough to develop the musculature of your abs, obliques, and, like Stu referenced, the illiac furrow.
Start doing them kneeling on the ground, then progress to doing them with your knees on a step. If you can build up to doing them standing you get 100 man points.
As for the abdominal vacuum, I think there is no real point in it as an exercise. I can abdominal vacuum with the best of them, and I've never once trained it. It was just an old school bodybuilding pose to show off how small they could make their waste. Today's bodybuilders don't seem to do it anymore.