I saw this over on Robert Burke's weblog.
Microsoft has released a powertoy that allows for raw image support in Windows for the following cameras:

-          Canon EOS 1D

-          Canon EOS 1Ds

-          Canon EOS 1D Mark II

-          Canon EOS 1Ds Mark II

-          Canon EOS D30

-          Canon EOS D60

-          Canon EOS 10D

-          Canon EOS 20D

-          Canon EOS Digital Rebel (300D)

-          Canon EOS Digital Rebel XT

-          Canon PowerShot G2

-          Canon PowerShot G3

-          Canon PowerShot G5

-          Canon PowerShot G6

-          Canon PowerShot Pro1

-          Canon PowerShot s30

-          Canon PowerShot s50

-          Canon PowerShot s70

 

-          Nikon D1

-          Nikon D1x

-          Nikon D2H

-          Nikon D2x

-          Nikon D70

-          Nikon D100

-          Nikon Coolpix 8800

-          Nikon Coolpix 5700

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Note that other models of cameras may work, but have not been explicitly tested by Microsoft.