Yes, it's a 64-bit version of Vista. I downloaded the installer again, just to confirm. If I run it normally, the install goes straight from the license acceptance agreement page to saying that DirectX has installed ("Installation Complete"), with nothing really happening in between. If I run as admin, the a new error dialog appears: "You must be running Windows 98, Windows Millennium edition, Windows 2000, Windows XP, or Windows Server 2003 family to install the DirectX 9.0." Switching to compatibility mode to run as Windows XP doesn't change things, since the installer still recognizes that I'm not running one of those OS versions.