If possible, think about the arrow like it having a shadow.
The distance between the arrow and the shadow is his height, so, to shot the arrow, it will have a arching trajectory, right?
Now, you'll need a math of this trajectory, the arrow will have mass and gravity, so, depending of the angle you shot your arrow, you'll need this math or something like it:
<img src="http://www.fisica.ufs.br/egsantana/cinematica/parabolico/parabolico2.gif" border="0" />
<img src="http://www.fisica.ufs.br/egsantana/cinematica/parabolico/Cine_14.gif" border="0" />
<img src="http://www.fisica.ufs.br/egsantana/cinematica/parabolico/Image478.gif" border="0" />
<img src="http://www.fisica.ufs.br/egsantana/cinematica/parabolico/Image1879.gif" border="0" />
<img src="http://www.fisica.ufs.br/egsantana/cinematica/parabolico/Image1880.gif" border="0" />
<img src="http://educar.sc.usp.br/sam/parabola.gif" border="0" />
I did an arrow arching for a old RPG game have about 4 years, and what I remember is that I did an invisible shadow, who give the real trajectory and speed of the arrow, and an arrow flying, going up and falling relatively to the shadow.