DNF system requirements have been announced by Gearbox

Duke Nukem Forever Minimum System Specifications

OS: Windows XP/Vista/7
CPU: Intel Core 2 Duo @ 2.0 Ghz / AMD Athlon 64 X2 @ 2.0 Ghz
RAM: 1 Gb
HDD: 10 Gb free
GFX RAM: 256 MB
GFX: nVidia GeForce 7600 / ATI Radeon HD 2600 or better
Audio: DirectX Compatible
[Minimum requirements are the bare minimum to get the game playing. In some cases you may even need to reduce the screen resolution.]

Duke Nukem Forever Recommended System Specifications

OS: Windows XP/Vista/7
CPU: Intel Core 2 Duo @ 2.4 Ghz / AMD Athlon 64 X2 @ 2.6 Ghz
RAM: 2 Gb
HDD: 10Gb free
GFX RAM: 512 MB
GFX: nVidia GeForce 8800 GTS / ATI Radeon HD 3850
[Recommended requirements are often listed as the system you would require to get the game running at a constantly good frame rate with graphical features turned up possibly to maximum, possibly on a large screen resolution etc. These can sometimes be expensive dream machines. However, you do not always need such a powerful machine to get the game to a playable and fun state. See below]

Game-Debate Requirements for Duke Nukem Forever:
o OS: Windows XP/Windows Vista/Windows 7
o CPU: Intel Core 2 Duo E4500 2.2GHz, AMD Athlon 64 X2 Dual Core 4800+
o RAM:2GB
o GFX RAM: 512 MB
o GFX: NVIDIA GeForce GT 240, ATI Radeon HD 3850 or better
o Hard Disk: 10GB space free
o Audio: DirectX 9.0 compatible sound card
[Game-Debates Requirements are what we think you can get Duke Nukem Forever running comfortably on. For example, you may not be able to turn anti-aliasing on but the game will still play and look just great at your standard resolution. We will adjust these requirements based on your feedback and they will power the system requirements tool on the game page]