Lines across finished video

I am hoping someone here can help me, i convert my dvd's the old way using smart ripper, dvd 2 avi, cdex (for the audio) and then put them together in virtualdub.
i have been doing it this way for years and felt no need to change as the results are always good. Only thing is on the last few films i have done i get king of distorted lines across the screen width ways.
i use divx to encode them and set it at 1500kbs & have the picture size @ 640 x 320

anyone come acros this before? as i said, its worked fine this way for years!

edit : Ignore this post please, done a school boy error and was setting my picture ratio for widescreen when the input dvd was 4:3....dope :-(