The CPP-GMR drive essentially changes the structure of drive heads. Current drives come with a tunnel magnetoresistance head. In these, an insulating layer sits between two magnetic layers. Electrons can tunnel through the layer. Precisely controlling the tunneling ultimately results in the 1s and 0s of data.
PC world is indicating that the new drives will be available in 2009. This makes more sense in order for hard drives to keep more market share from up and coming memory technology like Flash or NRAM and others.