You could either go the sophisticated route and store the messages in a database, or just put them in a text file and read/write them with fopen().
Depends on whether you need to keep them archived well, and if you are displaying a lot of them at once and have to manage which ones get displayed.
<?php
if ?submitcomment
{
store/write it with MySQL or text file
}
Display all the comments
?>
Show the HTML submission form.
Hope that helps!
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