I guess you already know this but STEAM has announced some system requirements on their website. its like this:
- OS: Windows® XP / Windows Vista® / Windows® 7 (only)
- Processor: 1.8 GHz Intel® Core™2 Duo E4300 or 2.4 GHz AMD Athlon™ 64 X2 4600+ (2.6 GHz Intel® Core™2 Duo E6700 or 3.0 GHz AMD Athlon™ 64 X2 6000+ or better recommended)
- Memory: 1.5 GB Windows XP
2 GB Windows Vista & 7. (4 GB recommended)
- Graphics: 256 MB DirectX® 9.0c-compliant video card with Shader Model 3.0 or higher (see supported list)*
- DirectX®: DirectX 9.0c-compliant
- Hard Drive: 12 GB
- Sound: DirectX 9.0c-compliant, 5.1 Surround sound card recommended
- Peripherals Supported: Windows-compatible keyboard, mouse, optional controller (Xbox 360® Controller for Windows recommended)
- Multiplayer: 256 Kbps or faster broadband connection
- Internet: Temporary broadband connection required for one-time product registration at first launch, permanent broadband connection required for multi-player.
- Supported Video Cards at Time of Release:
- ATI Radeon™ HD 2000 / HD 3000 / HD 4000 / HD 5000 / HD 6000 series
- NVIDIA® GeForce® 8 / 9 / GT 200 / GT 400 / GT 500 series.