As far as I know you only have to use the "Capture Video" if you are down loading from a tape. If you are referring to Import DVD titles then thats different. If the files are already on your PC you should just be able to point straight at them.
However if the video is a .vob file you will have to convert it into something that Pinnacle can edit such as an avi or mpg format as .vob files are not supported by Pinnacle. At least not the version I have. (v10.
Edit********
I just realised my answer doesn't make sense if you can already play some of the video.
Good luck.