Back in February I talked about the lack of RAW image support in Windows Vista and the inability to install the Microsoft RAW Image Viewer because it worked only for Windows XP. Vista uses a new modular design that allows camera vendors to add their RAW image codecs to the operating system, but that wasn't available in the first few months after Vista's launch. The Microsoft Photography blog keeps track of these changes, and it looks like the situation has vastly improved in recent months. Nikon, Canon, and Pentax have all released RAW image codecs for Vista.
One problem I have found is that the Canon codec doesn't cover some of the older Canon RAW formats with .CRW extensions, which were used on the original Canon Digital Rebel. It also doesn't let you export the images to .TIF like the old Microsoft RAW Image Viewer, so you'll still need to have your own RAW image conversion software. But that isn't a problem since most RAW-supporting cameras have at a minimum some basic software that does the conversions and other useful things like color balance and exposure adjustments. The Vista RAW codecs allow the Windows shell to display the thumbnail images and allows you to use Windows Photo Gallery to quickly view the images.