Website - Path

[eluser]WebbHelp[/eluser]
Hi!

Sry, I couldn't find any good title, but I write my question here:

How can I do if I want to that the visitors only will write: http://www.site.com/
To access the page, and I don't want them to write index.php?
Follow question = I want to; when you write the adress to the website, I want that you only need to write the path to the directory like:
http://www.webpage.com/dir then a file will run.

Summery:

That you only need to write http://www.website.com without index.php
AND
If you are writing the path to the website with a dir ex: http://www.website.com/dir then a file will automatically be runned.