As the 2P says - if a site allows directory listing you can view it, if not it is forbidden.
One other tool which can help you find files / pages on a website are search engines.
try google
site : overclockers.co.uk
(remove the spaces around the : )
It won't return much but try the 'similar pages'.
You can also use a web crawling software and set it off on a sites homepage.
Beware of the webmaster though. If you crawl too fast, or look dodgy your IP could be banned (not that that particular measure helps much).
Check out:
xenu link sleuth