Already installed error

Hi I’m new to wordpress so forgive if the terminology is wrong
I’m running Mac OS 10.6 and I just want to install wordpress locally, just to function on a test site. My site http://simplycolette.com is working fine.

I’m having trouble following the documentation. I was following this: http://codex.wordpress.org/Installing_WordPress_Locally_on_Your_Mac_With_MAMP and got to step 4 which leads me to do: http://codex.wordpress.org/Installing_WordPress#Famous_5-Minute_Install

If I want to do this all locally what is the dbusername, username, and password to fill in the wp-config.php file?

when i test out the install.php I get:

‘.__(‘Already Installed’).’

‘.__(‘You appear to have already installed WordPress. To reinstall please clear your old database tables first.’).’
‘);} switch($step) { case 0: case 1: // in case people are directly linking to this display_header(); ?>

ReadMe documentation at your leisure. Otherwise, just fill in the information below and you’ll be on your way to using the most extendable and powerful personal publishing platform in the world.’), ‘../readme.html’); ?>

error) ) wp_die($wpdb->error->get_error_message()); display_header(); // Fill in the data we gathered $weblog_title = isset($_POST[‘weblog_title’]) ? stripslashes($_POST[‘weblog_title’]) : ”; $admin_email = isset($_POST[‘admin_email’]) ? stripslashes($_POST[‘admin_email’]) : ”; $public = isset($_POST[‘blog_public’]) ? (int) $_POST[‘blog_public’] : 0; // check e-mail address $error = false; if (empty($admin_email)) { // TODO: poka-yoke display_setup_form( __(‘you must provide an e-mail address.’) ); $error = true; } else if (!is_email($admin_email)) { // TODO: poka-yoke display_setup_form( __(‘that isn’t a valid e-mail address. E-mail addresses look like: username@example.com’) ); $error = true; } if ( $error === false ) { $wpdb->show_errors(); $result = wp_install($weblog_title, ‘admin’, $admin_email, $public); extract($result, EXTR_SKIP); ?>

I hope this all makes sense.
thanks for your help in advance