#get latest package and check md5sum

wget http://wordpress.org/wordpress-2.9.1.tar.gz
md5sum wordpress-2.9.1.tar.gz
lynx -dump http://wordpress.org/wordpress-2.9.1.md5

#if md5sum is OK (should be 3af6bfaac37faa6ba58294f3de29c311 ), then continue 

tar -zxf wordpress-2.9.1.tar.gz
cd wordpress
cp wp-includes/compat.php /replace_your_wordpress_directory_here/wp-includes/compat.php
cp wp-includes/post.php /replace_your_wordpress_directory_here/wp-includes/post.php
cp wp-includes/version.php /replace_your_wordpress_directory_here/wp-includes/version.php
cp wp-includes/default-widgets.php /replace_your_wordpress_directory_here/wp-includes/default-widgets.php
cp wp-includes/class-simplepie.php /replace_your_wordpress_directory_here/wp-includes/class-simplepie.php
cp wp-includes/functions.php /replace_your_wordpress_directory_here/wp-includes/functions.php
cp wp-includes/user.php /replace_your_wordpress_directory_here/wp-includes/user.php
cp wp-includes/wp-db.php /replace_your_wordpress_directory_here/wp-includes/wp-db.php
cp wp-includes/formatting.php /replace_your_wordpress_directory_here/wp-includes/formatting.php
cp wp-includes/script-loader.php /replace_your_wordpress_directory_here/wp-includes/script-loader.php
cp wp-includes/class-json.php /replace_your_wordpress_directory_here/wp-includes/class-json.php
cp wp-includes/http.php /replace_your_wordpress_directory_here/wp-includes/http.php
cp wp-includes/meta.php /replace_your_wordpress_directory_here/wp-includes/meta.php
cp readme.html /replace_your_wordpress_directory_here/readme.html
cp wp-admin/wp-admin.css /replace_your_wordpress_directory_here/wp-admin/wp-admin.css
cp wp-admin/includes/file.php /replace_your_wordpress_directory_here/wp-admin/includes/file.php
cp wp-admin/includes/upgrade.php /replace_your_wordpress_directory_here/wp-admin/includes/upgrade.php
cp wp-admin/includes/image-edit.php /replace_your_wordpress_directory_here/wp-admin/includes/image-edit.php
cp wp-admin/includes/update-core.php /replace_your_wordpress_directory_here/wp-admin/includes/update-core.php
cp wp-admin/includes/template.php /replace_your_wordpress_directory_here/wp-admin/includes/template.php
cp wp-admin/theme-editor.php /replace_your_wordpress_directory_here/wp-admin/theme-editor.php
cp wp-admin/edit-attachment-rows.php /replace_your_wordpress_directory_here/wp-admin/edit-attachment-rows.php
cp wp-admin/options-general.php /replace_your_wordpress_directory_here/wp-admin/options-general.php
cp wp-admin/upload.php /replace_your_wordpress_directory_here/wp-admin/upload.php
cp wp-admin/upgrade.php /replace_your_wordpress_directory_here/wp-admin/upgrade.php
cp wp-admin/wp-admin.dev.css /replace_your_wordpress_directory_here/wp-admin/wp-admin.dev.css
cp wp-admin/options.php /replace_your_wordpress_directory_here/wp-admin/options.php
cp wp-admin/css/global.css /replace_your_wordpress_directory_here/wp-admin/css/global.css
cp wp-admin/css/global.dev.css /replace_your_wordpress_directory_here/wp-admin/css/global.dev.css
cp wp-admin/install.php /replace_your_wordpress_directory_here/wp-admin/install.php
cp wp-admin/update-core.php /replace_your_wordpress_directory_here/wp-admin/update-core.php
cp wp-admin/maint/repair.php /replace_your_wordpress_directory_here/wp-admin/maint/repair.php
cd ..