I'm a little bit confused by what you are trying to do. Are you trying to edit the video? Cut from scene to scene? If that's the case you'll need some digital video editing software. This can be done with software as cheap as Quicktime Pro or AVI Edit, or as expensive as Adobe Premier or Final Cut Pro (Mac Only).

If you want to change the pixel dimensions your movies render at, you can control that in the Animation Settings dialog under the Animation menu.

Hope this helps.