Tony's right (both in elaborating on the cause of my problems and the download location).

The builder image that gave me trouble is: http://empeg.com/downloads/car2-builder.upgrade
linked to from http://empeg.com/support.html and the Drive Upgrade guide at riocar.org.

I've been away from the boards for a while, so it's taking me a bit to catch up... has the topic come up of asking for an open sourced version of 3.0? I know there are a number of members here with the skills to contribute to it if given the opportunity. Without any more official development, it'd be wonderful if we were able to work on it ourselves.