diff -ur drupal-cvs/includes/bootstrap.inc drupal/includes/bootstrap.inc
--- drupal-cvs/includes/bootstrap.inc	2006-07-16 19:24:35.000000000 -0700
+++ drupal/includes/bootstrap.inc	2006-07-16 19:23:50.000000000 -0700
@@ -647,6 +647,12 @@
       // Initialize the default database.\
       require_once './includes/database.inc';\
       db_set_active();\
+      $result = @db_query("SELECT name FROM \{system\} WHERE name = 'system'");\
+      if($result && db_result($result) == 'system')\
+      \{\
+        header("Location: install.php");\
+        exit;\
+      \}\
       break;\
 \
     case DRUPAL_BOOTSTRAP_SESSION:\