http://www.fckEditor.net/
and download the latest version of the editor which is a Zip file. Open the Zip file and unzip the entire installation into any of your Web directories so you have fckEditor subdirectory underneath your Web root. If you have a WebControls virtual folder (ie. c:\inetpub\wwwroot\WebControls) it should look like this :

The editor contains many related pieces in this folder hierarchy including javascript files, images and stylesheets, but the editor is self contained and knows how to find all of these components on its own as long as the directory exists.
That's it. Once the control you can use the wwWebFckEditor control to configure editor instances on your form.
When you use the wwWebFcKEditor control you can specify the location of the library using the EditorBasePath property.