preemptive HTTP authentication

Does anybody know how to preemptively authenticate HTTP authentication?
(meaning HTTP authentication without filling in user_id/password in prompt)
I have tried using 'Header("Authorization: Basic QWxh-------");', but no luck.

I am currently trying to combine mod_auth_mysql authentication and my customized PHP athentication.
After PHP authentication, I would like to set mod_auth_mysql authentication( which use HTTP authentication), so that it would not prompt for user_id/password, again. - when I try to access folder that is protected by mod_auth_mysql authentication.

HTTP Authentication seems to be relying on
HTTP_SERVER_VARS["PHP_AUTH_USER"] and HTTP_SERVER_VARS["PHP_AUTH_PW"]
variables to check if it's authenticated.
I have tried using 'http://user_id URLassword@www.thesitename.com
, but old Netscape browsers does not work well with this.

If you have any idea about this, could you send email to this address: Jturtle@netzero.net
Thanks.