Use this:
PHP Code:
$fuserinfo=$DB_site->query("
SELECT user.usertitle,user.avatarid,usertextfield.signature,avatar.* FROM user,usertextfield
" . iif($vboptions['avatarenabled'], "LEFT JOIN " . TABLE_PREFIX . "avatar AS avatar ON(avatar.avatarid = user.avatarid) LEFT JOIN " . TABLE_PREFIX . "customavatar AS customavatar ON(customavatar.userid = user.userid)") . "
WHERE user.userid='$comment[commenter_id]' AND usertextfield.userid='$comment[commenter_id]'");
Untested