I got tired of messing with this, so I made some changes to the basic layout, and it fixed the problem.
These particular pages are technical ones, using tables for layout to make sure everything aligns, since mis-matched numbers could cause problems. The table had two columns, everything in the left column displayed as it should, but the right column with the AdSense div float was awful. Text on top of text, text on top of images, h3 text out of place, and despite validating with zero warnings, that's what I got.
I split the right column into separate cells, three on one page and two on the other, and now everything is just fine. No emulate code necessary.
The only thing I can figure is that another div in that same cell was causing a problem. Div float is a basic and it seems IE ought to get it right, since it's been a problem since IE5? IE6? It would be nice to know what the problem is, for future reference, since IE9 will be out at some point (likely with a slew of new problems, too!)
Hopefully I can get some work done, now, after wasting a good part of the day yesterday on this. Thanks to those who offered advice.