I checked on my Windows 7 PC. I've got 11 folders called "iTunes" (note the capital T), and 0 folders called "itunes".
I assume they aren not on a locked disk (both my c:-drive and my p:-drive are in use when I use Firefox), but I didn't check the write permissions for all 11 folders. That's easy to do. Either check the permissions in the folder properties, or copy a file into it (delete it afterwards).
I just started getting this message when I open Itunes - "The folder "itunes" is on a locked disk or you do not have wriet permission for this folder". Any help please?