hi mate check The individual folders are shared, as i dont think there are set to 'share with specific users'.
XBMC Lock issue on setting up SMB
ok, so this can be an issue if you dont have "simple file sharing" enabled. to enable that (or at least check that its correctly set up)
open up an explorer window (click "my computer")
tools -> folder options
select the "view" tab
and scroll to the bottom of the advanced settings area. at the bottom there should be a tick in the box that says
"Use simple file sharing (recommended)"
if not, tick it. that should mean the xbox can see the shared folder.
ive had similar problems, where the root shared folder was not accessable from xbmc - but sub folders which were also shared were. so id have a folder called
c:\downloads
which i could see from the xbox, but i couldnt stream from. a folder inside that which was also shared:
c:\downloads\tv shows\
would work just fine.
i hope this helps