func_object

1.Firstly, create a good sized room (300x300x300) and place your info_player_start and a light in there.

2.Create an exploding crate, giving it a func_explosive entity. Give the exploding crate a "health" of "150".

3.On top of that crate, create another regular crate, and apply the func_object entity to it. *NOTE* The func_object crate must be at least 4 units above the exploding crate (which is it's support). The top crate will drop down and sit on the exploding one when the map starts.

4. Compile your map and shoot out the explosive crate. The top crate will fall to the ground.

Thanx to Douglas Magee for submitting the info on func_objects.