Ejemplos:
Código PHP:
<?php
$number = 1234.56;
// english notation (default)
$english_format_number = number_format($number);
// 1,235
// French notation
$nombre_format_francais = number_format($number, 2, ',', ' ');
// 1 234,56
$number = 1234.5678;
// english notation without thousands seperator
$english_format_number = number_format($number, 2, '.', '');
// 1234.57
?>
Pero creo que lo que buscas es:
Código PHP:
$number = 750000.00;
$english_format_number = number_format($number, 0, '', '.');
echo $english_format_number; //750.000
EDIT: Para mas info:
http://www.php.net/manual/en/function.number-format.php