Urs - IE8 Beta 2 is coming in August and the final version a little later - read http://blogs.msdn.com/ie/archive/2008/06/03/ie8-beta-2-coming-in-august.aspx :
"...Second, make sure your site looks great in IE8; as you may recall, IE8 will use our new, more standards-compliant layout and rendering engine for strict doctype pages by default. This may cause IE8 to layout pages differently than IE7 did. If you haven't had a chance to test your pages yet or don't want to make changes yet, remember that you can have your site tell IE to use our IE7 layout engine for your strict doctype pages by adding the X-UA-Compatible http header to your HTTP headers or on a per document basis..." said by Tony Chor, IE8 Group Program Manager.
This is just a suggestion of what to do when the final version is out - to avoid confusion when IE8 breaks many parts of css / layout of moodle.