I am a relative beginner to the magic of using adjustment layers in Photoshop (I have ps7). I have taught my self a bit through tutorials, several books etc, but what I cannot manage is to make an adjustment layer that only works on the layer chosen, not on all of the layers below it.
ie. select sky, convert to a layer, add layer adjustment to this layer as a non permanent change. -> Adjustments also effect the layers below.

Can anyone point me in the right direction to manage this?

Many thanks. Julian