I fixed the float drop problem!
This problem was in the ordersteps addon to CWOA.
It was happening in IE6 and IE7 but not in Firefox. And only when checking out WITH an account.
The fix: in no_account.css, under #order_steps, change this line:
margin: 10px 10px;
to this:
margin: 5px 5px;

And if you haven't used the "@import ... " kluge mentioned directly above this post for the other 4 css files, you'll need to edit those files as well.

I guess that IE just needs a little more "breathing room".