Collision?

I have a problem :S

I have a gun which shoots a bullet to the mouse.

I have enemies.

The bullet is made with - graphics.lineTo(mouseX, mouseY);

Then is recalculated with - graphics.clear();

                                              graphics.lineTo(enemy.x, enemy.y);

You get the picture...

My problem lies here. The bullet when recalculated draws to the center of the enemy instead of the collision point and Ino why that is happening it because im using enemy.x and enemy.y.

How can I detect the exact collision point of the bullet on the enemy?

because then I can just draw line like this - graphics.lineTo(CollisionPointX, CollisionPointY);

Thanks