Camera Raw version 7.x is ONLY for CS6.
For CS5 you want version 6.7.
There's a dedicated Camera Raw forum where you should post:
Message was edited by: station_two
Camera Raw 6.7 for Photoshop CS5 will open your 5D Mark III files.
If you've made a mistake and you really have Photoshop CS6, then you need at least Camera Raw 7.1 to open 5D Mark III files, though I would suggest seeking out the current beta version (7.2RC) because they've fixed some image quality issues.
In any case, Help - Updates from within Photoshop ought to get you a version that understands your camera. Is that not working for you?
Thanks for catching my typo, Noel. I edited my post accordingly.