This was a bit of a pain to find via Google tonight so I figured I’d link to it and help others find it.
I finally dug up the Clearing Floats page on quirksmode.org. In the end setting “overflow: hidden” and “width: 100%” on the containing DIV took care of “containing” the floats to just that DIV. Awesome.
Did I mention I love quirksmode.org? Honestly. It’s one of the best JS resources there is.