Previously this has only been available on the MAc but today Adobe has gone public with the first Windows version. You have to register but it is currently free.
Project: Lightroom™ is Adobe’s effort to engage the professional photography community in a new way, giving you the opportunity to kick the tires and shape the feature set of a new tool being created just for you. Ultimately, we want Lightroom to be truly built from the ground up by photographers, for photographers, helping solve your unique workflow challenges
Adobe Labs - Project: Lightroom