I forgot to mention these in this post:
Holy cow! I want one of these so badly; too bad they were apparently hard to find even when they were still being made, around 1999.
There's more information here: http://www.waynesbooks.com/ADD.html#minibox
Also, I found out about these initially through a review at RPG.net: http://www.rpg.net/reviews/archive/classic/rev_1941.phtml