The listing on Steam notes the game’s multiplayer requires a headset, but the publisher has stated the listing was in error and Dark Souls PC does not support in-game voice chat. Dark Souls: Prepare to Die Edition for PC is out August 24.
Here are the requirements:
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