what should i Upgrade to play this game on medium settings

proedge

So im running on a amd athlon 64 3500, 2gigs of ddr ram and 6800gt geforce 256 megs. Now im thinking upgrading my video card too a 8600gt or better might be the ticket but i can also afford a new processor if that will help out alot. My motherboard can support 5200 duel core from what i read up on. Im not a computer wiz so I might just be talking out my Ass. Any Tips would be appreciated