question about run external programms in PHP

["SaEeDoS" <saeedos@xxxxxxxxx>]

Hi all , 
i have a question , how can i run an external programms from PHP , i
mean .  i have a php page let say like this :

<?php 
echo '<a href="c:\winamp\winamp.exe"> Click here to run Winamp</a>';
?>

how can i do that , i tried system() function and exec() but it
doesn't work ..
Thanks all