When I installed WordPress 3 and having the Twenty-ten theme, I also found that in older browsers, it will not display correctly as the center part of the page with the primary contents and sidebar are split, the page stretches DOUBLE WIDE with the header/footer on the right side and the main contents on the left. Anyway, it looks awful for people browsing on older browers as I sometimes do and as the poster above has witnessed. To fix it, I tweaked the following lines of code so that it would display correctly:
At line 83 of /wp-content/themes/twentyten/header.php, before <div id=”main”>, add the following:
<div style=”width:900px;position:relative;float:left”><!– corrects misaligned displays –>
At line 15 of /wp-content/themes/twentyten/footer.php, after </div><!– #main –>, add the following:
</div><!– corrects misaligned displays –>
And now everything should be peachy keen! Best wishes to whoever else might have this problem too. ??