Shooting Tethered with 5DII

Does anyone know how to get correct exposure when shooting tethered with a 5DII. When the camera is in Av or Tv mode you set the aperture or shutter value and the camera will give you the corresponding shutter or aperture value respectively when you mouse over the shutter release button, but when in manual mode there is nothing to help you determine the correct shutter aperture combination. Also when going into the Remote live view shooting window, there is a histogram button and another one next to it that appear grayed out. Any idea of how to get them enabled?

Thanks
Etienne

im just trying now - cant get it to show me histogram or internal light meter gauge, although ive never used it for anything other than mucking around and annong my wife with 200% closeups on her face.

Same for me. I never used it for anything, but now I think that it might come in useful for a project that I have in mind, where I might need to bracket my exposures by up to 4EV stops without moving my camera, and the best to do it is by using the tethered mode. But I think that it is quite useless if it doesn't give you a hint about the correct exposure value.