What do you mean by 'launch people around'?
You mean that if you go on top of a box, it launches you into the air? If so, just make water over your map, make the boxes, then on top of each box make a brush textured with AAATRIGGER.
Then select it and press ctrl+t and tie it to trigger_push.
Now set the Yaw Pitch Roll property to something (e.g. 30 0 0 - depends on the direction you want the player to be pushed).
Set the push speed to something or just leave it at 100 and that should be it.
...and that's the bottom line because Mate de Vita said so.
I made a man cannon once... on a surf map... i put it on a server and it was fun as hell
Make a AAATRIGGER brush and tie it to trigger_push. From there, you can use the little compos looking thing on the window that comes up. The direction corresponds to the top view, or if you want to use the down arrow thing and click up/down to push the player up/down. I suggest about a 1000 boost. 100 boosts would maybe push somebody about 50 units. you want 1000.