The mains thrust of their advice is that another program is interfering with the Steam installation. The writer describes a very odd function to the Steam installation, in that it first installs an earlier version of steam which it then begins to uninstall and overwrite with the current version. It is at this 27% point of the installation that the "hand-off" to the new installation is interefered with by "something". They mention two programs by name, Cybersitter, and Windowsblinds, (neither have ever been on my machine) which should be removed or disabled prior to attempting the installation of Steam.
They also go on to mention either a firewall or anti-virus program (mostly a firewall not allowing the modified program to run - a trojan or virus like behaviour).