Make sure your CHMOD is set so you have access to the Install.php file. Many of us change the permissions of it so "hackers" can't access it. If it's set to 000, change it back to 644 or something.
Also, make sure you are accessing the page properly. ie:
www.yoursite.com/yourxcartdirectory/install.php
You must type in the .php or it will continue to revert you back to your site. Hope this helps a little.
