Да собственно говоря все тут легко.
<?php
$mt="<html><head><meta http-equiv=\'Content-Type\' content=\'text/html; charset=windows-1257\'></head>\\n";
$mt.="<body>\\n";
$mt.="bla bla bla";
$mt.="</body>\\n";
$mt.="</html>\\n";
mail("to@mail.com","My Subject",$mt,"From: [email]null@pot.com[/email]\\nMIME-Version: 1.0\\nContent-Type: text/html; charset=windows-1251\'");
?>