Just do what everyone else does. AsRock Z77 Extreme 4 + Intel Ivy Bridge i5 + 8Gb DDR3 1600 RAM + Nvidia GTX670. You can put together a build based on these components for less than a $1,000 USD, and it will be able to run any game on maxed settings for the next couple years. It's overkill for Dark Souls, but if you're buying a computer, you may as well max out its ability within reason otherwise it will much more quickly become obsolete. This build is extremely "future proof".
I'd recommendvisiting reddit.com/r/buildapc for help and ideas.