Text (PC+errata): 4/2. ; Madness {1}{B}. ; When you cast ~this~, any player may sacrifice a creature. If a player does, counter ~this~. [Oracle 2009/07/08]
When this spell is played, the triggered ability goes on the stack on top of it. When the ability resolves, each player gets a chance (in turn order), to perform the action. If anyone does, then this spell is countered. [Planar Chaos FAQ 2006/12/13]
A player must actually pay the cost to counter it. Paying just part of the cost is now allowed. [Planar Chaos FAQ 2006/12/13]
