Index: install.php
===================================================================
RCS file: /cvs/drupal/drupal/install.php,v
retrieving revision 1.133
diff -u -p -r1.133 install.php
--- install.php	20 Sep 2008 20:22:23 -0000	1.133
+++ install.php	1 Oct 2008 00:24:33 -0000
@@ -69,6 +69,11 @@ function install_main() {
     require_once DRUPAL_ROOT . '/includes/cache.inc';
     $conf['cache_inc'] = 'includes/cache.inc';
 
+    // Check for PDO
+    if (!class_exists('PDO') || !method_exists('PDO', 'query')) {
+      install_pdo_error();
+    }
+
     // Initialize the database system.  Note that the connection
     // won't be initialized until it is actually requested.
     require_once DRUPAL_ROOT . '/includes/database/database.inc';
@@ -602,7 +607,6 @@ function install_no_profile_error() {
   exit;
 }
 
-
 /**
  * Show an error page when Drupal has already been installed.
  */
@@ -615,6 +619,15 @@ function install_already_done_error() {
 }
 
 /**
+ * Show an error page when PDO is not available.
+ */
+function install_pdo_error() {
+  drupal_set_title(st('PDO unavailable or invalid'));
+  print theme('install_page', '<p>' . st('We were unable to find the PDO class that is included in PHP but required for database access. <a href="@link">See the PHP PDO installation page</a> for instructions on how to enable PDO to continue with the installation process.', array('@pdo' => 'http://us.php.net/manual/en/pdo.installation.php')) . '</p>');
+  exit;
+}
+
+/**
  * Tasks performed after the database is initialized.
  */
 function install_tasks($profile, $task) {
Index: includes/bootstrap.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/bootstrap.inc,v
retrieving revision 1.228
diff -u -p -r1.228 bootstrap.inc
--- includes/bootstrap.inc	20 Sep 2008 20:22:23 -0000	1.228
+++ includes/bootstrap.inc	1 Oct 2008 00:24:34 -0000
@@ -1017,6 +1017,13 @@ function _drupal_bootstrap($phase) {
       break;
 
     case DRUPAL_BOOTSTRAP_DATABASE:
+      // Check for PDO
+      if (!class_exists('PDO') || !method_exists('PDO', 'query')) {
+        if (!function_exists('install_goto')) {
+          include_once DRUPAL_ROOT . '/includes/install.inc';
+          install_goto('install.php');
+        }
+      }
       // Initialize the database system.  Note that the connection
       // won't be initialized until it is actually requested.
       require_once DRUPAL_ROOT . '/includes/database/database.inc';