It is possible to add a timing system?

[zuhane1]

On my game I'd like to add a little system where the character stands with a javelin and a red line scans up and down. He would be in the bottom-right corner with the enemy in the upper-left. A red laser sighting would rotate by scanning from the bottom of the screen to the top. I was wondering if there was some way to then make the javelin fire in that direction once your pressed a key. I'd like to have it so you have to get the aiming correct and then hit the enemy to hurt/destroy it.

If you can help me I'll be most greatful. I don't know ho I can repay you... make another stupid game maybe?