If you haven't heard, the new Web SKU is a special, low-priced version of Windows that is focused exclusively on Internet-based Web serving. We've added a lot of new features and support for hardware compared to the old Windows 2003 Web edition. For more details about the SKU, check out Bill Staples' blog post at http://blogs.iis.net/bills/archive/2008/04/15/windows-web-server-2008-and-sql-server-2005.aspx.
One thing to note is if you want SQL Server 2005 on Web SKU. The installer blocks on Windows Web Server 2008 but we are providing a patch that will allow you to proceed with the installation. Before attempting to install SQL Server 2005, please download and install the patch from the Download Center page found at: SQL Server 2005 Installer Hotfix for Windows Web Server 2008 x86/x64.