hi auxiv.
It is not so easy.
But you can do it by editing the template (dirname)_inc_eachpost.html like:
<{if $post.poster_uid != 0}><a href="<{$xoops_url}>/userinfo.php?uid=<{$post.poster_uid}>"><{/if}><{$post.poster_uname}><{if $post.poster_uid != 0}></a><{/if}>
<{if $post.poster_uid != 0}>
<{if $post.poster_rank_title}>
<img src="<{$xoops_upload_url}>/<{$post.poster_rank_image}>" alt="<{$post.poster_rank_title}>" title="<{$post.poster_rank_title}>" />
<{/if}>
<{* <{$smarty.const._MD_D3FORUM_POSTERJOINED}>: <{$post.poster_regdate_formatted}> *}>
<{if $post.poster_from}><{$smarty.const._MD_D3FORUM_POSTERFROM}>: <{$post.poster_from}><{/if}>
<{$smarty.const._MD_D3FORUM_POSTERPOSTS}>: <{$post.poster_posts_count}>
<{if $post.poster_is_online}><{$smarty.const._MD_D3FORUM_POSTERISONLINE}><{/if}>
<{php}>
$member_handler =& xoops_gethandler( 'member' ) ;
$groups = $member_handler->getGroupsByUser( $this->_tpl_vars['post']['poster_uid'] , true ) ;
foreach( $groups as $group ) {
echo $group->getVar('name') ;
}
<{/php}>
<{else}>