Using espeak of ubuntu in php through System command

[tushar]

Hi !!
I use xampp on ubuntu 8.04 . I have installed it as mentioned and everything works fine : apache, mysql and php.
I have just one problem. When i try to use following command in my php script.

System ("espeak -f <inputfile> -w <outputfile>");

it doesn't work. It displays nothing.

Although when I use System command to execute 'ls' like

System("ls");

It works fine. That means I am getting problems in executing espeak only.
espeak is an inbuilt engine in ubuntu for text to speech conversion.
A script like <?php System("espeak hello"); ?> should produce an output sound saying hello. But nothing happens with xampp.

Tell me if something needs to be changed in the configuration files of xampp.
I need to execute espeak through php script.
Guys i really need to do this. provide me a solution as soon as possible.