Hi All,
I think people are getting confused by the very similar terminology here.
The install-media-* is what is required to build a PCMCIA/CF/USB that can be used to completely reformat a RE and return it to a factory default state. This image is a complete media image, therefore it has to be 'installed' onto the external card using the 'dd' command exactly as described on the webpage from which you download it.
The jinstall-* and the jbundle-* are software upgrade packages. The jinstall-* invokes a slightly more complete upgrade process, which is sometimes useful/required when upgrading between major versions (e.g. where the underlying kernel is upgraded, too). In general, I use the jinstall-* anyway because it is cleaner (the jbundle-* can invoke a slightly lighter - less intrusive - upgrade process, which should be fine for minor upgrades).
Rgds,
Guy