That's the D&D supplement that has the game stats for the action figure characters in it. It's written for the Mentzer version of the basic game, the one with the nice colorful boxes and the Larry Elmore cover artwork. (RPG geekdom calls it "BECMI D&D", after the titles of the boxes: Basic, Expert, Companion, Master, Immortal.) I do have a lot of affection for those rules, but I think I might use the 4th edition framework for it.
Yeah, I think I'm really doing this.