MP4 video editor recommendations ?

Went back and re-read your first post. Looks like you need the AVC Any Video Converter so you can read and work with the mp4 files.

To use on XP

[Official] Free Download DVD & Video Converter, Video Enhancer AI, YouTube Downloader, Video Editor, Video Recorder for Windows and Mac

Scroll down quite a ways to the freeware section, as they want to sell you other products first.