Here's the current best estimate for what id Software will be aiming for. Obviously this is subject to change.

CPU: Intel Pentium 4 2.8 GHz, Intel Core 2.0 GHz, AMD Athlon 2800+ or better
RAM: 1.5GB
Video Card: NVIDIA GeForce 6800 GT, ATI Radeon 9800 Pro or better
VRAM: 256MB of Graphics Memory
Storage: 12GB
Sound Card: DirectX 9.0c Compatible
ODD: DVD-ROM
DirectX: DX9.0c
OpenGL: Yes. Unknown version.

And the recommended system requirements:

CPU: Core 2 Duo/Athlon X2 or better
RAM: 1.5GB
Video Card: NVIDIA 7800 Series, ATI Radeon 1800 Series or better
VRAM: 512MB of Graphics Memory
Storage: 12GB
Sound Card: DirectX 9.0c Compatible
ODD: DVD-ROM
DirectX: DX9.0c
OpenGL: Yes. Unknown version.