Having been a lurker here for a while, I have a great deal of regard for AlanF, and I would rather be on his side in any discussion! But with all due respect, I would disagree with his position.
The key point is that a God who is "outside time" does not make predictions. One could say that this God knows what we will do before we do it; we could also say that this God knew what everyone in the Universe would do, before it was ever created.But both of those statements are missing the point... because they're still applying temporal terms to God.
In other words, the spacetime continuum, as AlanF aptly pointed out, appears static to God. But this is not because it is static, but rather because God can see all points of time at once. Not only "can," but "must" and "does". Because if God were to make a choice to see some things at one time, and not at another, that would imply that he was inside time!
I hope that this makes sense. It's a concept, like hyper-dimensionality, that can only be described logically, but cannot be grasped intuitively, because humans have no experience of being outside time.
I also don't claim that this concept is provable, by any means. I simply claim that it's not falsifiable. Whether one actually believes in free will and in prophecy are entirely separate questions. :)