Where did the site.xml at the end of the URL come from? The correct URL is the one that Abhijit posted - browsing there looks like repository contents.
What URL did you give for the m2e plugin? The correct one is
http://download.eclipse.org/technology/m2e/releases. (Note that you can no longer obtain the old m2eclipse plugin, or at least I haven't been able to find a URL for it.)
And if I recall correctly, Galileo should have the Eclipse Marketplace. If it does, try using the Marketplace to install the plugin.