If you are not sure which image to use, the most commonly used image is 5040_530510190.zip
This file is suitable for all 50xx and 55xx series replaytvs.
This one will allow CA and IVS on 55xx series replays see http://replaytvupgrade.com/caandivsin5500.htm for info.
Use the other files if you know what you are doing.

NOTE: replay5040.rtv.gz WILL NOT DOWNLOAD USING INTERNET EXPLORER 6 OR EARLIER
This is a bug (or feature) in IE. Use another browser or use ftp if you are experiencing problems downloading it.