There are a few small HTML errors in the Fresh Bananas theme. Found with http://validator.w3.org
It doesn't have the right doctype. It's XHTML 1.0 Strict, while I think it should be XHTML 1.0 Transitional.
The list in the sidebar is missing an ul-starttag and an ul-endtag. Opera and Mozilla correct it while rendering, but MSIE6 doesn't.