Thanks for that, Mark. Yes, I think they use a quicktime DV codec.
By "export" do you mean "render as" ? I tried this, and the resulting file is 7% larger than the original, so I'm guessing will result in even more work for vegas. Is this not the case?
I cannot drag 400 files into vegas separately and render them all, so will look into this TMPGenc you mention. It's a shame sony don't have a batch converter- how does everyone else batch convert their files for editing in vegas? I assume this must be a common problem.
Update:
I have just tried TMPGenc as you suggested, but it does not recognise the quicktime DV format. It gives the error message "could not open the video part of the file clip24.dv".