What do you mean by duplicate results? As for how it works, it’s a google search for url’s that contain “wp-login.php and that have “WordPress > Login” in the title, which should indicate exactly one WordPress 1.5 installation, and may also find WordPress versions less than 1.5
Well, some results from google show any number of duplicates; you get the message at the bottom of a page which states something about there being more results but many of them are duplicates of those already shown. I’ve never done what you’re doing there, so I just wondered how you KNOW it’s “exactly one WordPress 1.5 installation”.
Idle curiosity…. google’s famous for duplicate results on their search pages….