HP Question: How much did the Order know about the prophecy?

I would guess that Dumbledore only told them that there was an object of great importance that needed guarding. I don't think he would've told them any more than that, because the more people who knew about it, the more likey the information could get out to Voldemort. Arthur Weasley was attacked while guarding a door, so I don't think he even necessarily knew what was inside. The whole point of the Department of Mysteries is that no one really knows what goes on inside. So I would guess Dumbledore was very vague with the Order and that they followed his orders without even really thinking about it, because he's Dumbledore.