Microsoft released a new Camera Codec Pack for Windows 7 that will allow you view Nikon RAW (NEF) files directly in Windows Explorer or Photo Gallery without a third party software. Here is a list of supported Nikon cameras: D100, D1H, D200, D2H, D2Hs, D2X, D2Xs, D3, D3s, D300, D3000, D300s, D3X, D40, D40x, D50, D5000, D60, D70, D700, D70s, D80, D90, P6000.
The Camera Codec Pack can be downloaded directly from this link.