u can just wrap the code in <if condition="$show['member']"></if>
to be :
Code:
<if condition="$show['member']">
<if condition="$show['avatar']"><td class="alt2"><a rel="nofollow" href="member.php?$session[sessionurl]u=$post[userid]"><img src="$post[avatarurl]" $post[avwidth] $post[avheight] alt="<phrase 1="$post[username]">$vbphrase[xs_avatar]</phrase>" border="0" /></a></td></if>
</if>