FYI, IE 6 SP1 is about to be released been released:
It's interesting that in the highlights, they suggest going to quirks mode
if things look different-- as opposed to fixing any newly-apparent problems
with the code.
Standards compliance issues
Internet Explorer 6 SP 1 offers considerable improvements in standards
compliance. In some cases, this may cause HTML content to look
differently than in previous versions of Internet Explorer. Many of
the changes causing the largest compatibility problems are implemented
only under a specific <!DOCTYPE> declaration in the HTML. If you see
rendering problems, try removing any <!DOCTYPE> declaration in your
code, and check the Developer Center for more information on these
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