Okay I worked this out ;) but only after breaking the pages!
I used the supplied hotpot.php, having renamed the moodle hotpot.php, to install hotpot.
Then everything broke, i.e. no information appearing on any page other than header!
So I renamed supplied hotpot.php and renamed the moodle hotpot.php back.
Everything now runs okay, except that I haven't fully tested hotpot - oh well~!