php_ini configuration file mail function

Can somebody plaese tell me how to set up the php_ini config file to send mail when my server requires authentication. I am using windows and have set SMTP and smtp_port ok but get this error

Warning: mail() [function.mail]: SMTP server response: 550 Relaying denied - This server requires Authentication

The regular mail function of PHP doesn’t work if you need to authenticate w/ the SMTP server. You need to use PEAR’s Mail interface.

See here: