Verbatim:

> In Mac OS X, keychain files are stored in ~/Library/Keychains/, /Library/Keychains/, and /Network/Library/Keychains/, 

source: http://en.wikipedia.org/wiki/Keychain_(Apple)

*edit*
Sorry, I didn't understand that you were asking for the login password...

For that, there is [this similar question](https://superuser.com/questions/197508/where-are-mac-user-account-passwords-stored) elsewhere, with a good answer...