When trying to score headers you have to cross the ball somewhere between the 6 yard box and the 18 yard line (so the 'keeper won't come out and get it). And what I do is head the ball in the direction that it is moving (eg If I'm crossing from the left, after crossing, I hold down UP + RIGHT + D) to head in the upper right corner of the goal. The 'keeper ALWAYS (100%) misses and you get a goal. One may find it strange that you head the ball in the direction that its going because its somewhat normal to head it the opposite direction (in real football that happens) to catch the 'keeper wrong footed but in FIFA 2000 he gets it. So I tried heading it in the same direction as its moving and it works. This is a 100% scoring opportunity unless of course you try real hard to miss.