Installation notes for specific platforms
From Joomla! Documentation
Need to add a couple of simple sentences to standard web Joomla 1.5 installation method. Almost all application installations require the user to edit the configuration.php or equivalent file to put relevant user/db/password/email information. Well, the Joomla Web method actually creates the configure.php file at the end of its use - and if there is already a configure.php file in the root directory the web installation will throw an assortment of errors. There are many, many folks who are hitting this problem (check the forums). So, the following needs to be added to the documentation: "If you opt for the web method of installation you must NOT have a file named configure.php in the site root directory because the installer creates that file when it has completed running."