You can find information on the Image Manger in the following online help article http://www.telerik.com/help/aspnet-ajax/image_manager.html.
The ImagesPaths property is available in the Lite version of RadEdiotor for MOSS.
As it is explained in the article that you mention in your post, here is more ditailed explanation of the ImagesPaths property.
Lets open the SubSite1 ConfigFile.xml and set the following images path:
The ImageManager will load the SiteCollection/SubSite1
If you set the path with slash the ImageManager will open the SiteCollection
If you do not set the editor's ImagesPaths
property the dialog will show all the libraries from the current Web.
Note that. you can refer libraries only from the current site collection.
the Telerik team