Microsoft has introduced a new codec pack giving Raw image support to Windows Explorer and Windows Live Photo Gallery. The codec pack is free to download and is compatible with most camera makes and models that can shoot in their respective raw modes.
There are about 120 cameras that are supported, and the codec comes in 32bit and 64bit versions.
You can see the story here: http://windowsteamblog.com/windows_live/b/windowslive/archive/2011/07/26/photo-gallery-now-supports-raw-format.aspx
And the free download (showing supported models) is here: http://www.microsoft.com/download/en/details.aspx?id=26829