I assume you are using Veg

I assume you are using Vegas 6, the last build of that version is 210. If you are using an earlier build, go to the Sony site and download the updated version first to ensure that the problem has been solved in the newer build. Additionally, the preferences that you are looking for are in the capture program within Vegas. Go to the capture program, the to options, preferences and look on the capture tab, enable dv scene selection is the first check box.

John