|Derek, thanks for your kind reply.|
I downloaded Windows Movie Maker, but for some reason I can't get it to recognize MP4, AVI, and WMV files so far. Says "can't open this file or the file is corrupted" or similar. I'll look for support on WMM, maybe tomorrow.
I have been able to use iStonsoft WMA to MP3 converter to convert files into audio WAV files. I can use Audacity sound editor to selectively amp up the hard-to-hear parts. Then I could possibly use a video editor (WMM or another if I continue to have trouble with WMM) to reinsert the amped-up audio. Still, it would be better to have a more direct route to get this done.
Thanks again for saying that WMM will allow selectively boost portions of the audio. I'll try it again when I'm more alert.