According to a news release, NASA and Microsoft will work together on the underlying technology to deliver the images. The release also describes how NASA will tap into its archive for the project:
"To further integrate the planetary data into WorldWide Telescope, Ames is developing a suite of planetary data processing tools. These software tools convert historic and current space imagery data into a variety of formats and images of the moon, Mars and other planetary bodies readily available for easy browsing and use by the general public, enabling the creation of enhanced educational tools for students and teachers."
WorldWide Telescope was launched last spring. Separately, Microsoft and NASA previously worked together to make images of the Kennedy Space Center, including the Space Shuttle on its launch pad, available via Microsoft's Photosynth technology.