Is there a good video tut for beginners about modelling with
reference textures in ZB4 ?
Although this tutorial was created for ZBrush 2, the principles remain the same in Z4: http://www.zbrushcentral.com/showthread.php?t=33916
Of course textures are now assigned to SubTools using the Tool>Texture menu and you can now use PolyPaint rather than texture. But the ideas are still as good today as they were then.