Hi, thanks very much for the clarifications; I'm beginning to see where I've been going astray.  Let me check one more thing, if you would be so kind.  If we attach a load of impedance ZS (which may be frequency dependent) across the secondary, then the equation

should hold, provided that the load is a linear system; these variables are the (complex) Fourier transforms of their time-domain counterparts such as IS(t) and VS(t).  

I'm asking this only because I think this is where I'm going astray; personally, I think that we should avoid complex quantities/phasors, at least in the initial sections for lay-people.  Transformers seem hard enough to understand without introducing complex voltages and currents; I suspect most people would feel confused by them.  Leibniz says that complex numbers are "amphibians caught halfway between Being and Non-Being"; do you measure an imaginary current with an imaginary meter? ;)

I'll stop by again in a few days; I need to read up some more before I can feel that I have a clue.  But I'm trying sincerely, and I hope you can hang on a little longer.