SimplePortal comes with a simple way to create an integrated portal page in a different location from your forum. In order for login/logout to work properly, this standalone portal page must be in the same domain as the forum it is integrated with.
The SimplePortal installation created a file called PortalStandalone.php in your forum directory. Copy this file to the directory where you want your standalone portal to be (not in the forum directory) and rename it as you wish (use index.php if you want it to be the default page for the directory).