os.exec on Windows
On Unix executing binaries is split into two stages - fork(3) to clone current process and exec(3) to load executable into address space. On windows there is only CreateProcess which does the same thing as fork+exec.
For portability your best bet is to use subprocess.Popen (which also does proper filename quoting on Windows unlike os.* counterparts) as in http://docs.python.org/library/subprocess.html#replacing-the-os-spawn-family