thanks for the extra information.
The HotPot question import script doesn't need an "install.php". You would have been fine just clicking on the "Continue" button at the bottom of the page you get to from Site administration > Notifications.
Anyway, you have sucessfully installed the software. Well done.
Although the HotPot activity module does not recognize HP5 questions, I have a feeling that maybe the HotPot question import script will allow you import HP5 questions into the Moodle question bank, as long as you import from the original ".jcl", ".jcw", ".jmt", ".jmx" and ".jqz" files, that is to say, you can't import from the htm/html files.
Please try that and let us know how you get on.