Overclock the CPU, my son plays it fine with 5400+ and a HD4890. It will run fine with lowered details. Your biggest hindrance at the moment is the 8500GT which was not a very good card to begin with.
I see. Thank you for taking the time to explain but wouldn't overclocking effect a graphic card on the long run? Anyhow don't worry about the 8500gt; it's definitely going to be replaced since it can no longer perform and of the fact that it is of 3 years old.