You need to have the td tags around the noavatar also:
HTML Code:
<if condition="$show['avatar']"><td class="alt2"><a href="member.php?$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><else /><td class="alt2"><img src="images/avatars/noavatar.gif" alt="No Avatar" border="0" /></td></if>