[kh99]

OK, I tried this plugin code:

global $vbulletin;
$vbulletin->options['select_groupid'] = "5, 6, 7";
$show['hidehack'] = is_member_of($post, explode(',', $vbulletin->options['select_groupid']));

(I added the line to set the option), then I added this in postbit legacy:

<vb:if condition="$show['hidehack']">Hidehack<vb:else />No</vb:if>

and that seems to work. So maybe you should try to see what your option string it set to. Maybe temporarily put $vboptions[select_groupid] in the template and see what's displayed?