Create a Zip with Kernel.system

Hey,

I'm trying to create a zipfile containing a lots of pictures that
where uploaded using attachement_fu.
I used rubyzip, and everything worked great until I used it to
compress a lot of files, then it produced a RangeError (from an
Array#pack call somewhere in rubyzip).
So with a little irc help, I found out I could use a system call
(something like: system("zip -g zipfile file_to_add") ) and it should
work.
It worked locally (mac ruby 1.8.6 rails 2.3.3), but not on my server
(same but linux).
But when invoking a ruby script (ruby zipper.rb), with a few dumy
system calls it works.
When logging the return value of the Kernel.system call, it returns
nil.

I'm near banging my head against the wall, please help.

Geoff