The jumpiness/frame skipping is almost certainly caused by aged hardware - the processor isn’t powerful enough to decode the video in real time. The best cure is a new computer (or at least a processor upgrade), but since you don’t want that the next best thing you can do is a conversion with VirtualDub.
M4S2 wasn’t designed to work in VirtualDub (it’s a DirectShow codec, not a VFW one), but there are workarounds for that. You can change the fourcc of the video file to a different flavor of mpeg-4 (DX50, DIVX, or XVID), or use ffdshow as explained in this thread http://www.stevesforums.com/forums/view_topic.php?id=47897&forum_id=14&jump_to=314996#314996 (Thanks to Chrus for the link.)
Once you manage to open your M4S2 file in VirtualDub, click video, compression. Choose a codec that’s not processor-intensive (for example cinepak or indeo 3), then click file, save as avi.
Of course the conversion will take *longer* than playback (since M4S2 can’t be decoded in real time, plus the time to do the recompression), but the resulting file should be play fine.
New Casio Camera. Casio records and plays beautifully on Camera. Files are avi in M4S2 format. Results in Win95 are jumpy, skipped frames with good audio. I don’t want to upgrade any of my PCs and I don’t want XP, upgraded hardware or not. How can I convert these to “play nice” on my old hardware? The old hardware can play lots of other files very well. TIA.