The "www" directory is simply a shortcut to the "public_html" directory and the others all control various settings and features of your account and generally should not need touching.
If you have Microsoft FrontPage Extensions installed on your account, there will be several more with names such as _vti_bin, _vti_cnf, etc.
If you do not use Microsoft FrontPage Extensions you can disable the feature from your control panel and these folders will be removed freeing up a little space on your account.