You don't want to convert forums, polls, moderators, and others?
'cause if you convert posts you'll have to convert topics and forums...
If you don't want to convert groups only, you can delete these lines :
/* Groups conversion */
$sqlGroups = mysql_query('SELECT * FROM ibf_groups') or die(mysql_error());
$i = 0;
mysql_query('TRUNCATE TABLE mybb_usergroups') or die(mysql_error());
while ($groups = mysql_fetch_array($sqlGroups))
{
$namestyle = $groups['prefix'].'{username}'.$groups['suffix'];
$isBanned = ($groups['g_view_board'] == 0) ? 'yes' : 'no';
$canView = ($groups['g_view_board'] == 1) ? 'yes' : 'no';
$dlAttachments = ($groups['g_can_msg_attach'] == 1) ? 'yes' : 'no';
$postThreads = ($groups['g_post_new_topics'] == 1) ? 'yes' : 'no';
$postReply = ($groups['g_reply_own_topics'] == 1) ? 'yes' : 'no';
$editPosts = ($groups['g_edit_posts'] == 1) ? 'yes' : 'no';
$deletePosts = ($groups['g_delete_own_posts'] == 1) ? 'yes' : 'no';
$deleteTopics = ($groups['g_delete_own_topics'] == 1) ? 'yes' : 'no';
$postPolls = ($groups['g_post_polls'] == 1) ? 'yes' : 'no';
$votePolls = ($groups['g_vote_polls'] == 1) ? 'yes' : 'no';
$usePm = ($groups['g_use_pm'] == 1) ? 'yes' : 'no';
$sendEmail = ($groups['g_email_friend'] == 1) ? 'yes' : 'no';
$calPost = ($groups['g_calendar_post'] == 1) ? 'yes' : 'no';
$cp = ($groups['g_access_cp'] == 1) ? 'yes' : 'no';
$supMod = ($groups['g_is_supmod'] == 1) ? 'yes' : 'no';
$userCp = ($groups['g_title'] != 'Guests' || $groups['g_title'] != 'Banned') ? 'yes' : 'no';
$upAvs = ($groups['g_avatar_upload'] == 1) ? 'yes' : 'no';
mysql_query("INSERT INTO mybb_usergroups VALUES('".$groups['g_id']."', 1, '".$groups['g_title']."', '', '".$namestyle."', '".$groups['g_title']."', 0, '', '', '".$isBanned."', '".$canView."', 'yes', '".$dlAttachments."', '".$postThreads."', '".$postReply."', '".$dlAttachments."', 'no', '".$editPosts."', '".$deletePosts."', '".$deleteTopics."', 'no', '".$postPolls."', '".$votePolls."', '".$usePm."', '".$usePm."', '".$usePm."', 'no', '".$groups['g_max_messages']."', '".$sendEmail."', '".$canView."', '".$canView."', '".$calPost."', '".$calPost."', '".$canView."', '".$canView."', '".$canView."', '".$cp."', '".$supMod."', 'yes', '".$userCp."', '".$upAvs."', 'no', 'no', '".$canView."', 'no', 'no', 5, 0, 'yes', 0, 'no')") or die(mysql_error());
$i++;
}
echo '<p class="message"><b>Groups : <span style="color: green;">Done</span></b> | Inserted rows : <b>'.$i.'</b></p>';
/* End of groups conversion */
But be carefull, basic members will be super moderators and some members could be banned after the conversion.
No converting groups causes problems.