404 Not Found WordPress 3.0.1 Installation Error

I am trying to installl wordpress 3.0.1 but got an error name 404 Not Found. here is a sample https://yourdomain.com/wp-admin/install.php

I am using the above mention URL but no results ?? I have checked each and every thing Database name, User name, Pwd and detail instruction but all in vain. Change file to wp-config.php and enter correct User name & Psd but all got 404 Error.

Can any one guide me in this regards. what to do now??