Games rely more on the graphics card than anything else.
For high resolutions or max settings you need lots of vram on your graphics card. 512mb or more.
You also need a powerful graphics processor. Not necessarily the fastest but at least the next one down.
I have an 8800gts w/640mb vram and The Crysis Demo is so demanding that my old 4800X2 only runs 75% on both cores because the graphics card can't run any faster.
Your 8500 would probably freeze up on that game.
You can turn the settings down to medium and if you still have trouble then turn down things like shadows, water, textures in that order.
That new 8800gt/512 is a great deal on a gamer card.