1. A content download system for downloading a content file and additional content using a window of a graphical user interface; the content download system comprising: a content site that presents the window, wherein the window: displays the download progress of the content file, displays user interface controls to allow selection of the additional content for playing or downloading, wherein the additional content is bonus material and the additional content has not been chosen to be downloaded or played by a recipient of the content file prior to the user interface controls being displayed, automatically plays at least a first portion of the additional content, in streamed fashion, while the content file is downloaded, and allows selection of a second portion of the additional content, via the user interface controls for playing or downloading, the second portion being different than the first portion; a content provider that serves as an origin server computer for the content file; and a third party download-service server computer that receives information on the content file, wherein: the third party download-service server dynamically selects the additional content from contents in an additional-content database, the dynamic selection being prior to the automatic playing of the at least a first portion of the additional content; the third party download-service server dynamically selects a third portion of the additional content from a plurality of contents after receiving the selection of the second portion of the additional content, and the third party download-service server computer provides the additional content, and the additional content is automatically correlated to the content file.