How do I make an object rotate towards a moving object?

I have a box which moves on the Z axis. This is the player-controlled cube.
I have a cylinder which rotates on the Z axis.
I want the cylinder to always look at the player.

Note: I don’t mind a little python. The more I use it, the more I learn it.

trackto actuator

Thanks

Here’s a couple kittens
http://farm2.static.flickr.com/1404/1036069307_c665ac52ae.jpg?v=0

I am sorry, I meant track to actuator. It is in edit object group. Also try to check 3D button