If you are using the latest version of Moodle 1.5, the hotpot module should already be on your Moodle site, so there is no need to download and install the hotpot module separately. From now on, the best way for you to get hold of the latest verion of the hotpot module is via CVS. (see the Moodle CVS instructions if you need more information)
I don't think the fact that you attempted to run the install.php script did any damage to your Moodle site.
all the best