Hi,

user/registrationinfo.tpl

There is:

{'Click the following URL to confirm your account'|i18n('design/standard/user/register')}
http://{$hostname}{concat( 'user/activate/', $hash, '/', $object.main_node_id )|ezurl(no)}

$object.main_node_id is always empty because the user object isn't published.

kernel/user/activate.php
should also be altered.

Best wishes,
Georg.