aspect ratio

I am not getting the correct aspect ratio out of tmpgenc. Here is what
happens:

I take a movie in AVI format. AVIcodec says it is DivX v3, resolution
544 x 288, and aspect ratio 16:9. I want to make a VCD out of it. So I
load it into tmpgenc, tell it that the source is 16:9 (why doesn't
tmpgpec know that by itself?). It automatically chooses a 4:3 output
which can't be changed. In output, I tried both full screen (keep
aspect ratio) and no margin (keep aspect ratio), and the results are
the same. Both give mpg results that are close, but playing them in
media player or windvd both show output that are a little too tall for
the width when put up side by side with the original.

Why is it not preserving the visual aspect ratio?

Thanks,
Irwin

Irwin Feuerstein