<?php  

$yazim = eregi_replace(" ","_",$ad);  
$aranan   = array ('ı', 'İ', 'ç', 'Ç', 'Ü', 'ü', 'Ö', 'ö', 'ş', 'Ş', 'ğ', 'Ğ');  
$degisme = array ('i', 'I', 'c', 'C', 'U', 'u', 'O', 'o', 's', 'S', 'g', 'G');  
$turkceyazi  = str_replace($aranan, $degisme, $yazim);  

echo $turkceyazi;  

?>