Working around problems with IE 7 is a tedious subject of discussion, so forgive me for this. Thanks to a #code4lib exchange between Jonathan Rochkind and Gabriel Farrell I learned about
overflow: hidden and Methods for Containing Floats.
I was having a problem with a page that worked fine in all browsers except IE 7. It looked like this, with the content of one div flowing out beyond its boundaries:
overflow: hidden to the CSS on that div fixed it:
And it still works in all the real browsers, too.