Even if you do 'use Perl for server-side scripting' that won't help you here because you haven't posted a single bit of PERL/CGI anywhere in that code. You have a JavaScript that is running on submission of the form that emails a message (which the user types in) to an email address (which the user also types in).
If you are really trying to do a server side form processing for an email delivery, then we can help you out (but this code won't help you out). However, if this really does have nothing to do with PERL and you just want to modify the existing script, then I'll move this to the JavaScript forum as that would be the most apropriate section...
Either way, can you clear up exactly what you are trying to do so we can better help you/point you in the right direction?