I thought others might find this useful, as I found it a very frustrating problem to solve.
Registax (and other software) will easily import the Y800 format AVI from the Imaging Source DxK cameras, but will choke on the BY8 formatted ones.
I initially recorded some clips in BY8 format (won't do that again!

), but in order to salvage the AVI files I got for use with Registax, I used the following procedure:
Here's what you need:
AviSynth - a frame server (basically an interface between the "real" AVI and the program you want to use)
http://avisynth.org/mediawiki/Main_Page
In AVISynth, you create a small script file, which opens the source AVI file using DirectShow (you can do all sorts of other cool stuff to the video at this stage as well, but none are relevant for the job I'm doing).
Script file I used is called "jupiter.avs" and is as simple as:
DirectShowSource("C:\Jupiter0006.av i",fps=30)
You then open registax, and select the type as "AVI", and then in the field for the file specification, type *.*, then find the "jupiter.avs" file, and open it. It is very slow on some parts of the operations (aligning is quite quick as per usual, but anything after that that relys on jumping around in the AVI file is painfully slow)
Still, if you don't want to lose the images taken, this was the only option.
It works because the codec is registered in windows (hence can play in Windows Media Player which uses the DirectShow interface). This may work with other strange codecs that mainstream programs might not know about.
Hope it saves someone else the few days of pain I went through looking for a solution (has been cloudy since I took the original images, hence why i didn't just take new images!)
Turbo