I know this isn't the answer you're looking for, but seriously get a better cpu, graphics card and more RAM. Even doing one of those things is going to improve your peformance. Other than that the most you can do with that hardware is just make sure your hard drives are defragged often, can't really imagine what else you can do when everything is at the minimum level on DX7.
EDIT: Don't even know what that GPU is tbh. All searches bring up apple and mac, in which case I would tell you to get a PC, lol. Plus this has nothing to do with cRPG general discussion, it's a tech post for Warband.