I want to take portal.php and move it to mydomain.com, while my forum is located at mydomain.com/forums. Is there a way to do that? By the way, assume I rename portal.php to index.php when moving to mydomain.com
You can out the portal.php wherever you want, and edit the path to the forums into it, I think it's line 21.
yup, and no need to rename it if you want to use it as your index page. Just edit .htaccess to set DirectoryIndex to include portal.php
If you already have an index.* pages in the domain root, just remove them. You could even edit .htaccess to provide a redirect to and direct links to index.* pages to the new portal.php.
This is how I built the new implementation of my site. Works great