You have to use TweakNT to trick it into being XP Home or Pro in order to install some apps that use the MSI Installer (NAV, NSW, PM, etc.). If you don't the installer will detect a server OS and will simply refuse to install.. During which state your OS is having an identity crises like this, some functionality will be broken, but I have just noticed it was only Windows Update, and may also be anything that you can normally download from WU. Similar OSes such as XP Pro & XP Home and 2000 Pro & 2000 Advanced Server won't have this problem..