Commons:Wikipedia Loves Art
The description of this project is at w:Wikipedia:Wikipedia Loves Art.
The important detail for Commons editors to know is this:
The photos will be uploaded by the participants to Flickr, and thence to Wikimedia Commons and Wikipedia, but photos should not be uploaded to Wikimedia until the museums finish notating the proper ID and credit line.
Please do not upload photos to Commons until word has been given that the museums have finished their annotation effort, which is necessary so that the photos have the right information and there are no accidental copyright violations. This will probably be sometime in March or April.