I can't imagine trying to get everything 'cleaned up' without the ability to FTP. You can transfer and rename via XBMC filemanager though. But, to get XBMC to show a thumbnail, there are two methods to add them manually: 1. For a folder and all its contents, label the image 'folder.jpg' (litteraly) and put it in the folder. 2. For an individual file, label the image the same name as the file and change the extension to.tbn. There aren't any size restrictions that I know of.