There've been lots of complaints about the MediaWiki installation script over time, and with good reason! We don't actually use it for Wikipedia since it doesn't fit our needs (centralized repository of scripts for over a hundred wikis with near-identical config), nor does it fit the needs of a lot of people trying to set up their own wikis, who often don't have shell access to their web servers or root access to the database.
I've checked in the beginnings of a new install script that doesn't require shell access, root database access, or a separate place to put the source files and the installation. You can just unzip the archive, copy the directory tree to your web space, and run the configuration script through the web like with any civilized PHP app with relatively minimal fiddling.
At the moment it can create a configuration file that works with an existing database, but doesn't yet do the database setup. I'll try to get that merged in from the old command-line install script tonight or tomorrow and release 1.2.0rc2 with it included.
(Tech note: we need to be sure that the maintenance scripts aren't dangerous to have sitting around.)
-- brion vibber (brion @ pobox.com)