Nevermind I fixed it. I ripped out my css until I figured out what the problem was - for some reason, for the first time in the history of my writing CSS, I used a percent in one of my div's margins. I removed it, added the appropriate padding instead, and the problem went away.

It's still yet another wierd bug that it took the DL list (or the form, but I'm accusing the DL) to tweak IE's handling of the margins. Meh.
-m