Well I certainly appreciate the calm views about this. I'll drain the oil today, pull the idiot head and see what happened.
I don't know why I was freaking out about this so much, you're all right, it's just clean water in a well-oiled motor, I'll dump it out and start over. New filter, new oil (I know I'll make a huge mess trying to separate the oil+water mix -- I was using cheap oil (Penzoil) for a change at 100 miles or so anyways) then I'll spin up the oil pump again.
If it's just a backwards/missing gasket problem, and I can find a gasket set locally, I may fire it up Monday.