Executing shell commands

Hi, I'm trying to write a front end for something and I want to be able to execute shell commands. I tried all of the pre-written functions and non of them would work. I setup a user that can sudo and then i set apache to run as that user. So, what I tried to do is shell_exec("sudo -s; reboot;"); but that didn't work, I also tried other numerous variations all of which didn't work (also using exec(), system(), passthru() ). If any one has any ideas how i can do this, please let me know. Thanks

Teren