Alan,
what kind of DVD you are trying to create PAL or NTSC? 4:3 or 16:9? these are the major qestion at first, and which CS-suite you are using?
depending on the tv-standart the sceens have different resolutions:
PAL: 720×576
NTSC: 720×480
but adobe changed some informations on the pixel-aspec-ratios from CS4 to CS5.
if you are working with square pixels, you have 1024×576 for PAL (16:9) or 864×486 for NTSC (16:9), but adobe has changed these values from CS4 to CS5.
now they are different, for example PAL has now 1050×576 – this is confusing, your right, and a lot problems came with that idea as well.
cheers
danny