UniveRSS is a 3D RSS feed reader for Windows Vista. It leverages the Windows Presentation Foundation and provides a stunning way of visualizing RSS feeds and their content. It introduces a full-screen 3D universe where galaxies represent the folders of your RSS feed directory, and the stars are represented by the spinning cubes that hold the feed information. Size and position of the feed cubes indicate how many unread items they contain.
The source code is also available.
Edit: UniveRSS may run on Windows XP having .NET Framework 3.0 installed. Needs to be downloaded via Internet Explorer only though.