It would count. To put it simply : Pires rolls to Henry - Play one - , Henry shoots to the goal - Play two - . The rules say a penalty must be converted in two "plays" if i'm not mistaken. Like, you shoot, keeper saves it, and the ball goes in, it's a goal. But you shoot, keeper saves it, it hits the post, hits his back and goes in : no go. I read that somewhere, and in some TV show some guys were saying that France's penalty against Brazil in 86 wouldnt count as a goal today, because the GK saved it, it hit the post, hit his back and then went in.
Anyway, i'm 100% sure it would count, although my explanation was rather pish.