Disable new user registration

Add into LocalSettings.php
$wgGroupPermissions['*']['createaccount'] = false;

Only administrator will be able to create a new account. To do this administrator should use special link: index.php5?title=Special:UserLogin&type=signup

Disable edit for unregistred users

Disable edit/create page without registration.

Add into LocalSettings.php

$wgGroupPermissions['*']['edit'] = false;

// Not necessary to disable this explicity: it requires the edit right
$wgGroupPermissions['*']['createpage'] = false;
$wgGroupPermissions['*']['createtalk'] = false;

http://www.mediawiki.org/wiki/Manual:User_rights