Index: wp-admin/install.php
===================================================================
--- wp-admin/install.php	(revision 12048)
+++ wp-admin/install.php	(working copy)
@@ -66,6 +66,12 @@
 			<td><input name="weblog_title" type="text" id="weblog_title" size="25" value="<?php echo ( isset($_POST['weblog_title']) ? esc_attr($_POST['weblog_title']) : '' ); ?>" /></td>
 		</tr>
 		<tr>
+			<th scope="row"><label for="user_name"><?php _e('User Name'); ?></label></th>
+			<td>
+			<?php if (username_exists('admin')) { echo 'admin <input type="hidden" id="user_name" value="admin" />'; } else { ?><input name="user_name" type="text" id="user_name" size="25" value="<?php echo ( isset($_POST['user_name']) ? esc_attr($_POST['user_name']) : '' ); ?>" /><?php } ?>
+			</td>
+		</tr>
+		<tr>
 			<th scope="row"><label for="admin_email"><?php _e('Your E-mail'); ?></label></th>
 			<td><input name="admin_email" type="text" id="admin_email" size="25" value="<?php echo ( isset($_POST['admin_email']) ? esc_attr($_POST['admin_email']) : '' ); ?>" /><br />
 			<?php _e('Double-check your email address before continuing.'); ?></td>
@@ -106,6 +112,7 @@
 		display_header();
 		// Fill in the data we gathered
 		$weblog_title = isset($_POST['weblog_title']) ? stripslashes($_POST['weblog_title']) : '';
+		$user_name = isset($_POST['user_name']) ? stripslashes($_POST['user_name']) : '';
 		$admin_email = isset($_POST['admin_email']) ? stripslashes($_POST['admin_email']) : '';
 		$public = isset($_POST['blog_public']) ? (int) $_POST['blog_public'] : 0;
 		// check e-mail address
@@ -114,15 +121,23 @@
 			// TODO: poka-yoke
 			display_setup_form( __('you must provide an e-mail address.') );
 			$error = true;
+		} else if (empty($user_name)) {
+			// TODO: poka-yoke
+			display_setup_form( __('you must provide a valid user name.') );
+			$error = true;
 		} else if (!is_email($admin_email)) {
 			// TODO: poka-yoke
 			display_setup_form( __('that isn&#8217;t a valid e-mail address.  E-mail addresses look like: <code>username@example.com</code>') );
 			$error = true;
 		}
+		// Don't allow a second administrator on a re-install
+		if (username_exists('admin')) {
+			$user_name = 'admin'
+		}
 
 		if ( $error === false ) {
 			$wpdb->show_errors();
-			$result = wp_install($weblog_title, 'admin', $admin_email, $public);
+			$result = wp_install($weblog_title, $user_name, $admin_email, $public);
 			extract($result, EXTR_SKIP);
 ?>
 
@@ -133,7 +148,7 @@
 <table class="form-table">
 	<tr>
 		<th><?php _e('Username'); ?></th>
-		<td><code>admin</code></td>
+		<td><code><?php echo $user_name; ?></code></td>
 	</tr>
 	<tr>
 		<th><?php _e('Password'); ?></th>