The good news: No fooling around required - WLW 2009 installs just fine on Windows 2008! Here's my install screenshots:   (I don't understand what "Mail" is or why the Photo Gallery is in here...) This is the build number from Help -> About showing the RC0 build number....

Dunno why but MSFT made a version checker in the installation wrapper for Windows Live Writer so that you can't install it on a Windows Server 2008 box. Oh sure, I know what you're thinking: "But why would you want to install WLW on a server?" Well, I wouldn't. But...