Hi
just in case anyone else is having this problem, I was able to download a plugin filter called 'ef_aspectratio' which can be applied to each clip and can set the display ratio to 4:3 or 16:9. The downside is that the final video has lost quality (presumably because of the applied filter), but if this isn't an issue for you, then this would work.
I'm going back to MS Movie Maker and trying to use a conversion facility that won't cause quality loss in that app (the reason I was trying VideoPad in the first place).
Thanks anyway.