Since you mention Medieval 2, I'd direct you to PC Gamer, who know a sight more than me. They recommend you have a 3GHz processor and 1GB of RAM. It sounds like you're probably there already. I recently bought an Nvidia 7900GTO and that copes quite happily with the Medieval demo, I don't have the game yet. Some people mentioned the keyboard - that's what I'd say. Get better peripherals, a really good display for example. That's the bit you actually look at so whatever you put in the box depends on that to be good. Like you said, the wheel changed your experience. It's the tools you use to interact with the computer that matter as much as what's in it.