php How do I start an external program running - Having trouble with system and exec

I'm running in a controlled, xp, intranet only environment and I need to start external processes from a PHP applications. (Backups, Reports etc.)

I can get system or exec to start processes that work silently. Here's a simple example

<?php exec ("echo hello > hello.txt");?> 

I can get it to execute a bat file that has no visible output.

I can't get any program that has a screen to run such as a report generator or notepad...

<?php exec ("explorer");?>

doesn't do anything. or same for system