That's not how you create a custom page in vBulletin. This is:
Create a template called "custom_somename" ( it must be prefixed with custom_ ) and put something like this in it:
Code:
$stylevar[htmldoctype]
<html dir="$stylevar[textdirection]" lang="$stylevar[languagecode]">
<head>
$headinclude
<title>Some Page Title</title>
</head>
<body>
$header
$navbar
Some Page Content
$footer
</body>
</html>
Then you can call it using:
Code:
http://www.yourdomain.com/forum/misc.php?do=page&template=somename