I've seen a number of forum threads and help files on installing WordPress in a sub-directory but I'm having difficulty figuring out how to install it in the root directory but use a different name for index.php (say wp.php). The reason I want to do this is that I have an existing website and index.php that I want to remain the start-up page for my website. (And I'm using plug-ins that require WordPress in the root directory).
So, how would I name the WordPress index.php home page to wp.php and keep everything working? I tried changing the Blog Address (URL) to my domain name and wp.php (which worked for the homepage but not all of the permalink re-writes). Any insight would be extremely helpful.