The built in interlacing in WC4 is not designed to be viewed at any higher resolution than 640x480 (the video itself is pretty much half that resolution again. THere's no way to turn off that interlacing in the DOS version of WC4 and it ends up looking awful when scaled up since the scalers also scale the interlacing lines.
If you play the windows version you can turn off the interlacing using a command line addition to the shortcut. Better yet, you can upgrade the videos for free to the DVD version.