Why would you want to disable the Cmd key mapping over to the Windows key (especially since there are a lot of shortcut keys that are now (in Win8) dependent on having the windows key available)?
If press Cmd+Tab for switch 2X Client window to any Mac OS app, then is run Start menu in remote Windows. I have 2X Client for Windows Server 2008 and don't need any WinKey features for Win8. I have temporarily solved this with application WinKeyPlus.