The folder /templates/mytemplate/jscript contains:

onload (folder) - contains only read_me.txt
jscript_imagehover.js
read_me.txt

So, you're saying to take the code from the jscript_imagehover.js
file, put the standard <script> code around it, and write as
jscript_imagehover.php ?

I'm curious as to why some people have gotten the zoom feature to work without having had to report to this, as apparently it's not really documented anywhere I can see.

I also went back and looked at the IH2 documentation. It says to copy the jscript files into the folder of whatever custom template you might be using. Does it then matter if you leave the jscript files in the template_custom folder where they were put during the install? My brief experiment shows no difference in lack of zoom behavior, either way, at least for me.