The way IE8 renders is different from previous versions. The asp:Menu assumes incorrect defaults with regards to the z-index of the menu items. The ASP.NET team seems to be working on a fix for this problem.
In the mean time, take a look here to learn how you can work around the issue yourself: http://blogs.msdn.com/giorgio/archiv...ite-issue.aspx
In your case, you can fix the Planet Wrox site as follows:
1. In MasterPage.master add a new DynamicMenuStyle item like this:
<asp:Menu ID="Menu1" runat="server" CssClass="MainMenu" ....>
<DynamicMenuStyle CssClass="DynamicMenuStyle" />
Next, in Monochrome.css for the Monochrome theme add the following selector:
I'll fix the live version of PlanetWrox.com....
Hope this helps,