Brick wall/head/bash time.
A couple of weeks ago I rendered a widescreen standard definition .avi to a 512k wmv (for emailing to someone)
It played in a 4:3 frame, stretched so I adjusted some settings, re-rendered and did it again. Displays fine and it is true widescreen (I can drop it into another Vegas widescreen project and it fills the preview).
Now I've come to do it again and I can't get the same result. Turning off "Stretch..do not letterbox" results in a letterboxed 4:3 image (as you might expect), I've played with lots of settings but I cannot figure (ie I have forgotten) what I did to get a 16:9 image.