edit template : SHOWTHREAD
find:
<div><img class="inlineimg" src="$stylevar[imgdir_button]/printer.gif" alt="$vbphrase[show_printable_version]" vspace="1" /> <a href="printthread.php?$session[sessionurl]t=$threadid" rel="nofollow">$vbphrase[show_printable_version]</a></div>
change to:
<if condition="$show['member']">
<div><img class="inlineimg" src="$stylevar[imgdir_button]/printer.gif" alt="$vbphrase[show_printable_version]" vspace="1" /> <a href="printthread.php?$session[sessionurl]t=$threadid" rel="nofollow">$vbphrase[show_printable_version]</a></div>
</if>
done!