Recessed pull-down attic stair
Right, sorry. I don't have my digital camera with me so I put together some simple sketches in MS Paint.
[The following paragraph is easier to understand if you have the bitmaps open while reading it.]
I don't know how understandable it is. Basically, all the weight of the ladder and door goes through the 2x4's, and the door is flush with the bottom of the 2x4's, so I think of them (the 2x4's) as representing the whole of the ladder/door combo. Before I put the 2x4's in, there was a hole in the ceiling 54.5" x 26.5" (seen as the outer rectangle in the first figure). I put in the two lengths of 2x4 on both of the longer sides, making the opening smaller. The bottoms of the 2x4's were 1.5" above the ceiling (they should have been flush). I then installed the ladder/door combo, attaching it to the 2x4's such that the bottom of the door was flush with the bottom of the 2x4's.
If any further clarification is needed, please say so. I might be able to get photographs tomorrow (Monday).