This is a zscript tutorial of the basic method of using the ZProject brush to transfer sculpting from one mesh to another. It uses the DemoHead and PolySphere ztools which are shipped with ZBrush 3. These should be in the ZTools folder for the tutorial to work.
Unzip the zip file to a suitable location, such as the ZBrush ZScripts folder. Then load the ZProject-Sculpt-Tut.zsc file using the Load button in the ZScript menu. (Press the Menus button at the top of the UI to get the ZScript menu to show.) A ZProjection Sculpting Tutorial button will appear at the bottom of the UI. Press this button to start the tutorial. When the tutorial has finished you will be able to continue ZProject sculpting the model.
Edit: I have now written a Clear Offset plugin to help avoid sculpting offsets with this method.
I hope you find it helpful.