Before I begin the main point, a couple of things:

1) Yes, I know this is an old topic, but, having nothing else to do, I was reading through the archives, thought it looked interesting, read it and came up with a couple of ideas of my own. If you want to flame me, or delete this post, that's up to you.
2) I apologise if I'm repeated anything anyone's already said, or if this would be better as a reply to one of the existing replies, but there's so many of them that it's hard to tell.

Anyway....

I think the best to explain free will would be to assume that god _isn't_ totally omniscient - maybe he can predict anything that happens as a result of physical laws, maybe even quantum mechanics, but he _can't_ predict what a "free agent" will choose to do. Additionally, free agents are able to make decisions by the same basic mechanism as god himself (whatever that is), although to an infinitely small extent (assuming that god is infinite).

I hope I've contributed, albeit belatedly, to this thread, assuming anyone can even remember it the first place :-).