Threading the Python interpreter

[MooJoo]

I've read that the Python interpreter is not thread-safe but are there 
any issues in creating threads that create new processes (not threads) 
that run new instantiations of python? What I'm doing is subclassing the 
threading.Thread and, in the run method, I'm making a call to os.system, 
passing to it another python script which then processes a file. When 
the call to os.system completes, the thread is finished. Here is a 
simplified fragment of code for what I'm doing.

from threading import Thread
import os

class MyThread(Thread):
   def __init__(self, fn):
      Thread.__init__(self)
      self.fn = fn

   def run(self):
      pyscript = '/usr/bin/env python script.py %s'%self.fn
      status = os.system(pyscript)

thr = MyThread('test.dat')
thr.start()
thr.join()

Since I'm running each python instance in a new process, I don't believe 
that there is a problem and, in my testing so far, I haven't encountered 
anything that would lead me to believe there is a potential time bomb 
here. Am I correct in my assumption this is OK or just lucky so far?