using exec/system function within php/apache app

hi... i'm trying to track down issues that i seem to be having with using exec/system shell functions within web/php apps on apache. i'm running php-5/apache2/rh8.0. i'd like to talk with anybody who's gotten the exec/system functions to work, to try to compare your setup vs. what i have... i can create a command line test that illustrates that php/exec works. however, when i try to create a short web test to trigger the exec, nothing is happening. i suspect that i might have a priv/permissions issue, although i have no real idea where to look to resolve the issue. any thoughts/pointers/assistance would be helpful... searching through google/apach/php hasn't given any solid leads.... thanks -bruce