$show['whatever'] is only available in certain parts of the script (although those 2 I'm not so sure about).
Code:
<if condition="is_member_of($vbulletin->userinfo, X)">This will show to people who are in the usergroupID X.<else />This will show to all others.</if>
is_member_of checks primary and secondary usergroups. If you just want to check primary:
Code:
<if condition="$vbulletin->userinfo['usergroupid'] == X">yeah</if>