Some more debugging is definately in order -- I need to track down precisely why it's not dropping the proper hidden parameters in the HTML -- but I think I'm missing something very obvious to anybody who's written a couple login mechanisms by now, but is horridly difficult to figure out the first time.
So, in an effort to learn from the past mistakes of others, I'm going on a quick FAQ/tutorial hunt. The missing element may well show up during said search.
I may not be able to finish this thing tonight, but I'm going to try like hell before I fall asleep, and tomorrow I'm going to try like hell again before I have to go to work.
I can do this. I just have to try harder and think harder.