If you want a specific Usergroup to see the link then use the Usergroup's ID in the conditional. Such as:
Code:
<if condition="is_member_of($bbuserinfo, x)">
<a href="/forums/article_form.php">$vbphrase[writers]</a></if>
Where "x" is replace it with the Usergroup's ID. If the ID = 9 then replace "x" with "9". You can also add ID's by adding a ", y" and so forth in the routine.