Minimum PC specs for Assassin's Creed III have been specified by Ubisoft:

Minimum System Requirements
• Supported OS: Windows Vista (SP2) / Windows 7 (SP1) / Windows 8
• Processor: 2.66 GHz Intel Core2 Duo E6700 or 3.00 GHz AMD Athlon 64 X2 6000+ or better recommended
• RAM: 2 GB (4 GB recommended)
• Video Card: 512 MB DirectX 9.0c-compliant with Shader Model 4.0 or higher (see supported list)*
• Sound Card: DirectX 9.0c-compliant (5.1 surround sound recommended)
• DVD-ROM: Dual-layer drive
• Hard Drive Space: 17 GB
• Peripherals Supported: Windows-compatible keyboard, mouse, optional controller (Xbox 360 Controller for Windows recommended)
• Multiplayer: 256 kbps or faster broadband connection

Supported Video Cards at Time of Release:
• AMD Radeon HD 3870 / 4000 / 5000 / 6000 / 7000 series or better
• NVIDIA GeForce 8600 GT / 9 / 100 / 200 / 300 / 400 / 500 / 600 series or better
• Laptop versions of these cards may work, but are not supported. These chipsets are the only ones that will run this game.

The PC version of Assassin's Creed III is due November 23, PlayStation 3 and Xbox 360 versions are out October 31, and the Wii U version accompanies that console’s launch on November 30.