Stuck on installation

Hi, I’m trying to install wordpress 3.0.5 on a debian machine running Apache 2.2.16, php 5.3.3-7+squeeze1. WordPress was originally installed in /usr/share (came with the Debian software). I’ve copied the /usr/share/wordpress directory and all contents to our Apache document-root/wptest directory, and set up a virtual host called wptest on the server. Following the ‘How to Install WordPress’ instructions, used mysql command-line directives to create a database, user/password and grant the appropriate permissions. But, when I try to install via a browser with the url wptest.com/wp-admin/install.php, I get a 404 page not found error.

I know the site is working, as I can set a default .html file as the startup document, and it displays. I can hit wptest.com/readme.html, and it displays. I know the user in mysql is good, in that I can access it from the command line. No errors in the apache error log, nor in the wptest error log. I believe install.php is beginning execution, but I never see the ‘WordPress Installation’ page.

Only things in the install.php between the sanity check and the display of the Installation page is 4 lines of php:

define( 'WP_INSTALLING', true);
require_once( dirname( dirname( __FILE__ ) ) . '/wp-load.php' );
require_once( dirname( __FILE__ ) . '/includes/upgrade.php' );
require_once(dirname(dirname(__FILE__)) . '/wp-includes/wp-db.php');
$step = isset( $_GET[‘step’] ) ? $_GET[‘step’] : 0;`

and I’m clueless.

Any pointers on where to look and what to do would be greatly appreciated.