Assuming you're past the point where you have a repository with files already under version control, you simply add in wherever you want the substitution to occur the variable name surrounded by $.

/* SVN: $Id$ */
/**
 * Short Description
 *
 * Long Description
 *
 * @package			mypackage
 * @lastmodified	$Date$
 * @modifiedby		$LastChangedBy$
 * @version			$Revision$
 */

Then you run the svn propset command in your working directory:

svn propset svn:keywords "Id Date LastChangedBy Revision" . -R

Remember, you need to set properties to all new files you add, this is NOT done automatically!

Related posts:

1. SVN Automatically Setting Properties
2. Backing Up Subversion Repositories Using svnadmin hotcopy