As I blogged about a little while ago, the Microsoft RAW Image Thumbmailer and Viewer application was released last week. You can download it from here. It doesn't install directly under Windows 2003 server as on my laptop, but it will soon :-)
Officially, you need Windows XP to run it though.
Update - Monday PM. Yes, it seems to work OK under Server 2003 - you're on your own though when it comes to support.... I do like that transparancy you can see in the screenshot below when you have the properties window open but not the active window.