There are two forseeable ways:
The first is to edit /includes/functions_login.php, changing the filename to whichever file you want:
PHP Code:
$vbulletin->url = $vbulletin->options['forumhome'] . '.php' . $vbulletin->session->vars['sessionurl_q'];
You could also set the [high]$vbulletin->url[/high] variable to your desired location via the
login_redirect hook location
However the manual code change will only alter logins from the forum home - The second part of that entire if statement refers to the url you logged in from - To alter that you will need to alter the code:
PHP Code:
$vbulletin->url = fetch_replaced_session_url($vbulletin->url);
$vbulletin->url = preg_replace('#^/+#', '/', $vbulletin->url); // bug 3654 don't ask why
By using the hook location you
should remove this from being an issue
Chris