MediaWiki 1.15.1 Installation
Can't write config file, aborting
In order to configure the wiki you have to make the config subdirectory writable by the web server. Once configuration is done you'll move the created LocalSettings.php to the parent directory, and for added safety you can then remove the config subdirectory entirely.
To make the directory writable on a Unix/Linux system:
cd /path/to/wiki chmod a+w config
Afterwards retry to start the setup.