I was not able to find a clear problem.....
In my experience it could be a few things....
, many times in older versions of IE forms will not display right. drop downs in particular....
The hidden PHP
... (using a Get instead of Post or something similar)
Quick question... why are you using a .html page?
The script that does all of the searching( found here
) contains php.
I suggest switching to either a .php extensions or going in and modifying your .htaccess file(assuming Apache) by adding the below.
RemoveHandler .html .htm
AddType application/x-httpd-php .php .htm .html
Let me know if you cannot change the page or the file and we will see if I can think of a work around to get everything up