Matt Cutts explains the difference between how Google interprets underscores and dashes in a URL.
Have a question? Ask it in our Webmaster Help Forum: http://www.google.com/support/forum/p/Webmasters?hl=en
Want your question to be answered on a video like this? Follow us on Twitter and look for an announcement when we take new questions: http://twitter.com/googlewmc
More videos: http://www.youtube.com/GoogleWebmasterHelp
Webmaster Central Blog: http://googlewebmastercentral.blogspot.com/
Webmaster Central: http://www.google.com/webmasters