[Admin]

Also using getavatarurl() adds an extra query whenever its run, so in a list with lots of members the page will really slow down.

Anyway, here's how you do it.
In memberlist.php, add this:

    if ($userinfo[avatarid]!=0) {
      $avatarurl=$userinfo[avatarpath];
    } else {
      if ($userinfo[hascustomavatar] and $avatarenabled) {
        $avatarurl="avatar.php?userid=$userinfo[userid]&dateline=$userinfo[avatardateline]";
      } else {
        $avatarurl="";
      }
    }
    if ($avatarurl=="" or ($bbuserinfo[userid]>0 and !($bbuserinfo[showavatars]))) {
      $userinfo[avatar]="";
    } else {
      eval("\$userinfo[avatar] = \"".gettemplate("postbit_avatar")."\";");
    }

right after this:

    if ($userinfo[homepage]!="" and $userinfo[homepage]!="http://") {

Now replace this:

  $users=$DB_site->query("SELECT *
                          FROM user,userfield

with this:

  $users=$DB_site->query("SELECT *,avatar.avatarpath,NOT ISNULL(customavatar.avatardata) AS hascustomavatar,customavatar.dateline AS avatardateline
                          FROM user,userfield
						  LEFT JOIN avatar ON avatar.avatarid=user.avatarid
						  LEFT JOIN customavatar ON customavatar.userid=user.userid

And now place $userinfo[avatar] in the memberlist template.