Okay, it looks like IE6 is throwing a real fit about the new layouts. See the very helpful screenshots in this comment.

I've given IJ-sitepage-body a width, so it should have layout and IJ-sitepage-nav should accept absolute positioning within it; apparently the problem is something more arcane.

If anyone has a copy of IE6 in easy reach and wants to poke at the problem, I'd hugely appreciate the help. The only copy I can get to is remote and I can't connect to anything /else/ while using it, which makes testing changes a bit of a trial.

Any ideas are welcome!

ETA: Height of the header is part of it; this... is going to be a pain. I might actually need to add a clearing div to the html code. More news as I can catch it.

ETA2: Triumph! Maybe. I think I've gotten it to play nicely with older IE, but if anyone has a copy of IE5 or 6 hanging around and could give it a test-drive once the code is live, that would be very helpful.