The <%--comment--%> is an asp/asp.net which would not work in html files.
As Dave has mentioned, you'll need to use a server scripting language if you want to do this, html is a client side scripting, so whatever in the file will be seen when you view the source.
check your hosting provider and see if it supports asp or php, if so you can rename the file to either and use their comment.
Check
http://www.tizag.com/phpT/comment.php
http://www.tizag.com/aspTutorial/aspComments.php