Luc, aka Begasus, from BeBug fame, wrote an introduction/tutorial to a new tool which can be found in ZETA 1.21, named MakeMe. MakeMe is a all-in-one type of application for developers, with it you can create your app, compile and package it, and more.

Begasus gives you a description of various stages he went through (and which developers will also go through), to create a ZETA theme, a very nice one I might add, I'll have to ask him to send me. Plenty of screenshots can be seen as well, so head over and enjoy the reading.