User Defined Startup Folders

From ZBrush Info

In Zbrush 3, you can customize your startup environment. If you use specific alphas, texture, materials and/or ZBrush plug-ins than you can place them in the ZStartup folder of your root ZBrush directory.

How To Use Startup Folders

Alphas

Simply place your grey scale 16 bit alphas in the ZStartup/Alphas folder.