Converting VOB files problem.

I found a VHS copy of an animation collection, which I've had transferred to DVD. Now I would like to select out a couple of the cartoons to share with friends.
I've downloaded the VOB files from the disk and tried converting them, but something's going wrong. I tried the simple method, renaming the file to WMA or MPEG, but in both cases the image was distorted on one of the cartoons I most want to share. I've tried converting to flv and avi through some commercially available programs, but these just reproduce the sound track - no image, just a blank screen.
I'm guessing that there's a codec issue involved, but how do I determine which codecs I need? I've just run Sherlock, which has given me a list of all the codecs installed, but I'm not techy enough to make sense of that.