Have just spend way too long trying to work out why xbmc could no longer connect to a win7 smb share. The solution after much head scratching, simply uninstall Windows Live Login Assistant. Why this application should block shares from xbmc is beyond me. I have no idea what I was thinking about when I recently installed the Windows Live software anyway, most of it easily replaced by better programs. The guys at xbmc.org made a nice post on their forum about win7 smb shares
, the windows live bug is mentioned there quite a bit.