Graphics: NVIDIA® GeForce® GTX 465 or higher, ATI Radeon™ HD 6870 or higher
DirectX: Version 9.0c
Network: Broadband Internet connection
Hard Drive: 14 GB available space
Sound Card: DirectX 9 sound device
Additional Notes: Controller support: Microsoft Xbox 360® Controller for Windows® (or equivalent) recommended
There's another set of system requirements floating around the Internet as well. It was first posted on the Namco store and then spotted by IncGamers. Those specs are virtually the same as the Steam listing. The only difference is that the Namco store requirements say the game requires 8GB of space instead of 14GB. Namco has since taken the specs off their store, though, which suggests that the Steam version is more accurate.
The first Dark Souls didn't get much extra mileage out of better systems due to the game's low resolution and locked frame rate. Developer From Software admitted last year that they had half-assed the PC port. However, DS2 will feature improved textures as well as an "enhanced frame rate mode." You won't have to rely on Durante to fix the game.
The PC version of Dark Souls 2 is also said to have better mouse and keyboard controls, a weak point in the previous game. However, as you can see with the system requirements, a gamepad is still recommended. I can barely play Souls games with a controller so I shudder to think what a mouse/keyboard playthrough would be like.