edit [skin1]/common_templates.tpl and add something similar:
Code:
{elseif $main eq "mainlogin"}
{include file="customer/main/login.tpl"}
Note, place your login form from, auth.tpl in customer/main/login.tpl
Now just create the login.php file, with something like:
Code:
<?
require "../smarty.php";
require "../config.php";
@include "./https.php";
require "./auth.php";
$smarty->assign("main","mainlogin");
$smarty->display("customer/home.tpl");
?>
Should do the trick
