attempting to primary login feature

[invitezone]

adding a rquirement to index.php

can I add something like this

require('auth.php')

to index.php?

Auth.php being a simple php login script that I want to use as a primary login feature before it allows anyone to reach the forum.

I have tried to add this but i get the following errors.....

<?php
require('sas.php')

gives me the error...
Parse error: syntax error, unexpected T_STRING in /home/invitezo/public_html/index.php on line 15
**********************
require('sas.php')
<?php

gives me the error...
Unable to add cookies, header already sent.
File: /home/invitezo/public_html/index.php
Line: 2

Im sure this is only something silly that I dont know, so I would appreciate any help.
If you need some more infor please ask.
thanks