[Zope] os module on different os's

I have a Zope application that runs on WinXP and Debian sarge without problems. I am using os.popen and popen2 to run locally installed applications and use their output in Zope (particularly aspell and diction). On Ubuntu Dapper and FC5 however, these os calls fail. Is there a problem with recent Distros and this module? Python version is 2.3 on all systems but I tried 2.4 on FC5 and that failed too. regards garry