You could use Cbox which is a simplified comments code:-
http://www.cbox.ws/
or use Wordpress which is blogging software that you can integrate into your web page, slimming it down so that it has just one simple comments box.
http://wordpress.com/ You don't have to use the themes.
Both the above enable viewers to see the comments, but if you want private comments use a form which sends comments to your email address:-
http://www.wickham43.net/formemail.php
or to a database:-
http://www.wickham43.net/formphptomysql.php
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.