There are a number of things that you can do in addition to stripping HTML tags.
Limit the length of the fields to an appropriate number of chanracters so that people don't SPAM SPAM ...
Don't display what people submit instantly so that they don't get the instant satisfaction of SPAM SPAM SPAMing your page. You can do some moderation.
Require user registration (I really donno how that fits into your needs or your users').
If you're the only one who would add records, you can use some authentication schema (.htaccess files if you're using apache).
Also, your script is not handling mult-line comments properly (I added one with 3 comment lines and each appeared separately). Are you using the CGI module to get your params?