You create a simple mail script to start off with
<?php
//set your vars for the mail
mail($To,$Subject,$Msg,$headers);
?>
And then work on your cronjob (unsure of how this works - ona Windows box) or set your scheduled task as below:
Use the Scheduled Tasks control panel, but don't use HTTP. Call PHP executable directly, with the path to your script as the parameter.
Start menu... control panels... scheduled tasks
Add scheduled task... browse... select PHP executable
Go to the new task, right click, properties, then change the 'Run' box to, for example
C:\php\php-cli.exe c:\path\to\script\called\mail.php
Hope that helps...