edit: missing pawn from sentence
You didn't quite state that right--every move something moves, so it is not possible to go 50 moves without moving anything. :-)
The rule is 50 moves without a pawn moving or anything being captured.
Also, it can be a draw, but it does not have to be. When the last 50 moves have been without a pawn move or a capture, the player on the move can claim a draw if he wishes, but does not have to do so.
Recently, FIDE added a 75 move rule. It is similar to the 50 move rule, except that it is a draw even if both players wish to continue the game. (They also did a similar thing with the 3-fold repetition rule, which like the 50 move rule is only a draw if a player claims it. There is now a 5-fold repetition rule that draws even if neither player wants to claim a draw).
In fact, the only irreversible move that doesn't reset the 50 move rule is castling (or losing the right to castle), as having the ability to castle technically changes the position.