I haven't worked with SMF forums before so I'm not entirely sure where you would or wouldn't be adding code. I would need to be more familiar with the file structure to know.
Here's what I see in the source code:
HTML Code:
<HEAD>
<Title>eMediNews Forum - Medical Forum for All</Title>
<META NAME="keywords" CONTENT="medicine, public, issue, forum, medical, health, doctor, information, eMediNews, nursing, paramedicine, paramedic, biomedical, expert, advertise, product, medical school, pharmacy, nurse, question, answer, professional,">
<META NAME="description" CONTENT="All-in-one medical foum for the public, health professionals and students. Get latest update on health-related issues. Great place for health professionals to interact and share their knowledge and experience. You may advertise your health-related sites and products in this forum for free.">
<META NAME="author" CONTENT="Dr. Teoh KA">
<LINK REV="made" HREF="admin@emedinews.com">
<META NAME="revisit-after" CONTENT="1 day">
<META NAME="distribution" CONTENT="Global">
<META NAME="robots" CONTENT="All">
<META NAME="rating" CONTENT="General">
<META HTTP-EQUIV="content-type" CONTENT="TEXT/HTML; CHARSET=ISO-8859-1">
<META HTTP-EQUIV="content-language" CONTENT="En">
<META NAME="abstract" CONTENT="All-in-one medical foum for the public, health professionals and students. Get latest update on health-related issues. Get experts' opinions on your questions on various aspects of health. Great place for health professionals to interact and share their knowledge and experience. We also provide a place for you to advertise your health products for free">
<!--All-in-one medical foum for the public, health professionals and students. Get latest update on health-related issues. Get experts' opinions on your questions on various aspects of health. Great place for health professionals to interact and share their knowledge and experience. We also provide a place for you to advertise your health products for free-->
</HEAD>
and right after it:
HTML Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"><head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<meta name="description" content="eMediNews - Index" />
<meta name="keywords" content="PHP, MySQL, bulletin, board, free, open, source, smf, simple, machines, forum" />
<script language="JavaScript" type="text/javascript" src="http://emedinews.com/Themes/default/script.js?fin11"></script>
<script language="JavaScript" type="text/javascript"><!-- // --><![CDATA[
var smf_theme_url = "http://emedinews.com/Themes/classic";
var smf_images_url = "http://emedinews.com/Themes/classic/images";
var smf_scripturl = "http://emedinews.com/index.php";
var smf_iso_case_folding = false;
var smf_charset = "UTF-8";
// ]]></script>
<title>eMediNews - Index</title>
<link rel="stylesheet" type="text/css" href="http://emedinews.com/Themes/classic/style.css?fin11" />
<link rel="stylesheet" type="text/css" href="http://emedinews.com/Themes/default/print.css?fin11" media="print" />
<link rel="help" href="http://emedinews.com/index.php?action=help" target="_blank" />
<link rel="search" href="http://emedinews.com/index.php?action=search" />
<link rel="contents" href="http://emedinews.com/index.php" />
<link rel="alternate" type="application/rss+xml" title="eMediNews - RSS" href="http://emedinews.com/index.php?type=rss;action=.xml" />
</head>
I can tell those weren't written by the same people. If you created the first code sample above then I wouldn't do whatever you're doing since it's just duplicating a section of code that should only be there once.
As far as the writing the meta description you're in luck since a good post was written a couple of days ago at SEOmoz on writing them.
Making the Most of Meta Description Tags
I'd need to know the way SMF is put together in order to know how to make them all unique too. It looks like SMF is currently set up to use the title of the particular thread or page as the meta description. There might be some settings in the administrative controls to set that up or it might need someone editing the files to make the change.
I'd sooner use the thread title as the page title (what's in between the <title></title>). You might only be able to set the forum to use the first 'x' number of characters or words as a meta description which would probably be fine.
I hope that helps some.