Literally the day of launch, Dark Souls mods hit the internet. One such mod allows users to fix the locked resolution.
Yes, there is already a mod for Dark Souls! Somebody going by the name Durante has provided a definitive fix for the locked internal resolution, allowing the game to up to run double the native resolution. He recommends to turn off in-game AA (anti-aliasing), though, which could improve your performance. Currently the fix is in stage 0.2 at the time of posting, here are a couple of before/after screenshots:
(Click to enlarge.)
Enjoy the mod my demon hunters, and please consider donating for this man’s effort.