not sure if this works but try the following:
leave the folder names as C,D,T instead of categories, detailed, thumbnails....if not just do a simple rename of the folders
move folders to the files directory, but do not move the images folder
now go to include/func/func.image.php and back it up before continuing...once backed up, edit the file and find the following in function func_image_dir($type)
Code:
$dir = $xcart_dir."/images/".$type;
change to
Code:
#if the files directory variable doesnt work, try to hardcode it in as "/files"
$dir = $xcart_dir.$files_dir."/".$type;