AimBow is a separate mod. As soon as you hold an arrow, an egg or a snowball, the cross (or whatever target aid your texture pack provides) in the middle of the screen is moved to the position where the arrow will hit the ground. The color is changed to red (no hit) or green (entity hit).
You can enable/disable bow auto aiming by pressing Y. If you enable autoaiming, this is an Aimbot for Minecraft.
How to install:
For Minecraft 1.8