Thanks, Paul.
The Arcsoft software was indeed put there when I ran the installation
CD for my Toshiba HD camcorder.
Both the DVD writer & the camera were purchased & installed around the
same time.
I've noticed that mp4's taken by the Toshiba camera don't seem to be
recognized by Windows Movie Maker, so maybe there's something
propietary going on. Dunno. I'll try uninstalling Arcsoft.

Thanks again! :-)