After killing the installation attempt, Firefly is in H:Program FilesFirefly Media Server, but there is no service to start or stop. The taskbar tool says that I need to be an administrator in order to install the software.
If I doubleclick on the file that appeared to hang, WindowsInstaller-KB893803-v2-x86.exe, it indicates that the service pack that I am running (Windows XP SP3) is newer than the update I’m trying to install.
When I try to reboot later, it appears that some application that was trying to uncompress files had hung, and I have to kill that process.