The help resource that you are referring to is for RadEditor for ASP.NET, not RadWindow. Indeed, some of the articles there can be applied to RadEditor for MOSS, however you will need to install RadEditor for MOSS first by following the instructions in the Installation and deployment
section of the RadEditor for MOSS documentation
As for enabling the image uploading, if the user has the appropriate permissions over a library, he will be able to upload in that library - RadEditor for MOSS' FileBrowser uses MOSS' security mechanism to enable the corresponding folders for the users.
the Telerik team