This video tutorial shows how to install FCKeditor using the WYSIWYG API module. WYSIWYG makes it easy to install the most popular content editors on a Drupal site.
Note: Click the 'full screen' icon (to the left of the volume control) in order to watch online at full 1024x768 resolution.
UPDATE: Please take note that newer versions of the WYSIWYG API module require that the editor files get placed in the sites/all/libraries folder. This folder probably doesn't exist on your web server so you should create it if it does not exist.