I am testing IE8 Beta and found that my WordPress site was no longer presenting correctly. Where the header was positioned by CSS has been moved. Microsoft sent out an email to developers on August 27, 2008 notifying them of the problem and gives a link to the fix.
How I Fixed My Site: Go to the header.php file and add the fix in after the head tag <head>:
<!-- Use IE7 mode -->
<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7" />