In a broadcast system in which computer data and other content are delivered from multiple content servers to multiple clients at least partly over a broadcast network, a transmission announcement system announces upcoming broadcast transmissions and instructs the clients on how to receive the broadcast transmissions. Announcement servers (which may or may not be the same as the content servers which serve the data for the broadcast transmissions) generate announcements containing information specifying how associated upcoming transmissions are to be delivered over the broadcast network. The announcement server makes the announcements available to the clients over the broadcast network or over a secondary link other than the broadcast network. As possible examples of the secondary link, the announcement servers might send the announcements to a multicast address over a public network, such as the Internet, or post the announcements at a publicly accessible site on a data network, such as a Web site on the Internet. The clients receive the announcements via the broadcast network or the secondary link. The clients filter the announcements according to predetermined criteria, keeping the announcements satisfying the criteria and discarding the rest. The client searches the announcements that are kept to extract information pertaining to retrieval of the broadcast transmission (e.g., a broadcast protocol, a broadcast locator, a transmission time, etc.). The client then tunes a broadcast receiver to the broadcast locator and launches a receiving application to receive the transmission according to the broadcast protocol.