CKEDITOR.config.baseHref
The base href URL used to resolve relative and absolute URLs in the editor content.
http://localhost/web01/cms/editor.php
http://localhost/web01/upload/
myeditor.config.baseHref = 'http://localhost/web01/upload';
html, body { height:100%; }
myeditor.config.height = '100%';

Re: Some questions regarding CKEditor 3.0
my workaround for now looks like this:
bofore I pass the content to the editor, a PHP routine changes all relative path to absolute path for all resources (even to images in the CSS file, like background-image:url(<path>);
And before saving the editors content back to database, I do the reverse changes...
Although it works it's not a nice solution: When you open the image dialog, there is the long absolute url shown. Also when you pass back a image from your file/image selector, you have to add a absolute url - not very nice at all, but it works at least...
Hope this helps,
Peter