Strange... I can't reproduce those errors, but sometimes I get a similar error message about some other not found templates. After refreshing the page these errors normally disappear.
The login forms and so on should work, make sure to update your _config.php as described in my post in the other thread (http://www.silverstripe.com/google-summer-of-code-forum/flat/1520?showPost=1553).
As usual, try a .../?flush=1 and a ../db/build?flush=1
If it still doesn't work tell me (try a var_dump of MemberAuthenticator->authenticate()), should be a member object or FALSE.