Well if you want usergroup 1/2/default code then you need something like this:
HTML Code:
<if condition="$show['avatar']">
<if condition="$post['usergroupid'] == X">
Usergroup X code here
<else />
<if condition="$post['usergroupid'] == Y">
Usergroup Y code here
<else />
<a href="member.php?$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>
</if>
</if>
</if>