This does work from a "shape of the video" point of view and has got me out of the deep stuff for a short dead line this weekend.
Thanks!
However 
This doesn't explain why when using "Same as input" does the converter change the aspect ratio.
Also by using the Portable Devices setting the quality is around half of that which my archos can handle.
Is there no way of keeping there 720x576 with 16:9 aspect ratio?
If not this will mean I have to re-encode my whole collection twice... Once for the Archos and once for streaming to the 37" LCD TV.
Not idea....