Help with Installing WordPress 1.5

I followed the instuctions but it does not work. This is the text that it comes up with:

Warning: main(/home/altherit/public_html/wp-includes/wp-db.php): failed to open stream: No such file or directory in /home/altherit/public_html/wp-settings.php on line 39

Fatal error: main(): Failed opening required ‘/home/altherit/public_html/wp-includes/wp-db.php’ (include_path=’.:/usr/lib/php:/usr/local/lib/php’) in /home/altherit/public_html/wp-settings.php on line 39