I had the same problem last weekend burning a sample video to IDVD.
It was working well a few weeks ago but now IDVD seems to be squishing
the footage vertically. There is a black bar on the top and bottom of the screen
and the fields are totally mangled. I was using 10bit footage.
I then tried other SD footage on my machine that was in a variety of
codecs; 8bit, pjpeg etc and also footage that was 486 high and 480 high.
Some of the footage was made in FCP some in After Effects. I had the same
results with everything that I tried. I then tried DV footage and that worked as it should.
-Sandy