Hey, AWR (just got your PM)!
There is indeed a product for this purpose (I did mine from scratch in Illustrator because a) I liked the challenge of measuring and drawing from scratch and b) I'm an idiot.
For the life of me, however, I cannot recall. It works in 2D and basic 3D as well. I saw it on a MacMinute.com story a good while ago (a year or so, maybe). And I know that Macworld magazine did a review of this product within the 12-16 months.
I am drawing a complete blank on this thing...but I want to believe it had the word "interior" in its name?
That might give you some things to search for, to narrow it down. I downloaded their demo back in 2004 or so and played with it, but decided just to do straight elevations and isometrics in Illustrator myself (for the above reasons).
If I come across this product - or suddenly remember the name - I'll post it here!