WordPress.org

1. Download the plugin.
2. Upload the plugin to your wp-content/plugins directory.
3. Activate the plugin.
4. Enter yout API key on the YoutTube Poster settings page. (get the key at http://code.google.com/apis/youtube/2.0/reference.html )
5. Once a valid key is entered you can post YouTube videos under the Posts heading on the admin page.

This plugin requires at least PHP 5. and SimpleXML

if you are on a hosting platform that defaults to PHP 4, but offers PHP 5 you can add this line to your .htaccess file:

AddType x-mapp-php5 .php or AddHandler application/x-httpd-php5 php

The first one worked for my 1and1.com accounts, and the second worked for my generic linux hosting with cpanel account.