With the future release of the PC version of Dark Souls, Dark Souls: Prepare To Die Edition on August 24th, system requirements have been revealed.
OS: Windows XP , Windows Vista, Windows 7, or newer
Processor: 2.6 GHz Dual-Core
Memory: 1 GB (XP), 2GB (Vista/7)
Hard Disk Space: 4 GB
Video Card: 512 MB RAM, ATI Radeon 4850 or higher, NVIDIA GeForce 8800 GT or higher
Sound: Direct Sound Compatible
At least the game isn't as demanding on the computer as most modern games are today, which can mean anyone with a decent computer can run Dark Souls pretty smoothly. For more details, you can check out the game's steam page here.