Applied to Sitecore V5.1.x.
In order to get a list containing all the folder items in the media library and use it as a source for the Multilist field, you can use the following approaches:

  • query:/sitecore/media library//*[@@templatename='Media folder'] - Returns all items and all subitems based on the Media folder template. Note that the templatename attribute is case sensitive.
  • query:/sitecore/media library/*[@@templatename='Media folder'] - Returns all items under the root of Media library based on the Media folder template.
  • query:/sitecore/media library//*[@@templatekey='media folder'] - Returns all items and all subitems based on the Media folder template. Here is another approach using the templatekey attribute.
  • query:/sitecore/media library/*[@@templatekey='media folder'] - Returns all items under the root of Media library based on the Media folder template.You may find this link useful as well: http://sdn5.sitecore.net/SDN5/FAQ/API/Lookups%20with%20XPath.aspx