THats usually the arguement. People who believe it God will claim that since God knows all, he knows our future, therefore it must be pre-determined therefore if I beleieve it doesn't matter what I do, or anything because its pre-determined and therefore I'll be okay and goto heaven or whatever it is you believe.
However, even the Bible states that God gave us free will. This would mean that we do choose our own destineys. But to put it in a less religious aspect think about it this way. If you believe in phsycics, does that mean that life is pre-determined? No. Why do people goto phsycics? To find out the future. If life was pre-determined, it should matter to you whats going to happen, its going to happen no matter what. People goto phsycics to hear there future. If they like what they hear they do whatever they can to make it happen. If they don't to do whatever they can to avoid it. If they still avoid it trying to make it happen well they just play it off as well I knew too much about my future.
Now I don't believe in phsycics, I do believe we were given free will....however I do believe in God and I do believe that when it says God know all, it doesn't mean he knows what choices I'm going to make to determin my own destiney, I believe it means that God knows all the possible outcomes of my choices. Meaning he knows what my destiney holds for me, should I choose to goto work, or should I choose not to show up at all. He knows both outcomes he knows what choices would come from that previous choice and the outcomes of all those choices. But he lets me make those choices for myself.