Starcraft 2 Wings of Liberty System Requirements

Operating System: Windows XP / Vista / 7
Processor: Intel Pentium IV running at 2.6 GHz or AMD equivalent
Memory: 1 GB of RAM (1.5 GB recommended for Vista and 7 users)
Hard Drive: 12 GB or more
Video Card: 128 MB with Pixel Shader 2.0 (GeForce 6600 GT or ATI 9800 PRO)
Sound Card: DirectX 9.0c compatible
Optical Drive: DVD-ROM running at 4X
DirectX: DirectX 9.0c
Input: Keyboard & Mouse

UPDATE: Recommended System Requirements

Operating System: Windows XP / Vista / 7
Processor: Intel Dual Core running at 2.4 GHz or AMD equivalent
Memory: 2 GB of RAM
Hard Drive: 12 GB or more
Video Card: 512 MB (GeForce 8800 GTX or ATI Randeon HD 3870)
Sound Card: DirectX 9.0c compatible
Optical Drive: DVD-ROM running at 16X
DirectX: DirectX 9.0c
Input: Keyboard & Mouse