I think your host has the wrong end of the stick.
You are not asking for Classic ASP to be enabled as it already is, what you need to ask them for is to enable Classic ASP to send error messages to the web browser, and for detailed error messages to be enabled in the Windows IIS web server.
This will allow you to see a detailed error message with the line number etc. instead of the generic 500 error. This detailed error message will point us straight to the issue.
The instructions that they gave to alter the .htaccess file or the PHP.ini file would be for Apache web servers running PHP. Web Wiz Forums does not run on Apache web servers and uses Classic ASP, so this is incorrect information, as you would need to be on a Windows IIS web server to run Web Wiz Forums.
We are primarily a web hosting company, and probably give better support then the one you host provided you. If you moved your website over to us we should be able to get it up and running in minutes.