This really should be in a phpMyAdmin support forum, but if I recall correctly you don't just go to:
localhost/phpMyAdmin/install/
you'll probably need to call the install/configuration file, which would be more along the lines of localhost/phpMyAdmin/install/config.php or similar.
also, make sure you set your database variables in the configuration file before you try and install it, or it'll throw an error and ask you to set them anyways, unless you've got root with no password open. :/