Not sure what invisionboard is, but I have a rough idea of some things that are going on, and maybe that will point you in the right direction:

1) accessing a directory returns list of files, not an index:
You need to configure the web browser to not allow listings of the directory
This is highly dependent on the web server you are running, but the second suggestion I am giving you should fix the problem, but you still need to figure out how to tell it that.

2) accessing a directory returns a list of files, not an index:
You need to tell your web server that index.php is a valid index file (then it won't default to showing the directory). So look for a directive or configuration that allows you to tell it what the index file is (look for index.html or Default.htm, those are the two common ones)

/nebulus