sounds like the server has the default character set in the php.ini file set to windows-1252, you can try over riding that by adding the following code at line 1L
<?php ini_set('default_charset', 'UTF-8'); ?>
or you may need to try setting the header for the page:
<?php header('Content-Type:text/html; charset=UTF-8'); ?>
if those 2 fail, you will nee to contact the host to have them change the servers default character set to allow UTF-8 form data to be posted.