The new multiprocessing module is not being installed:
$ python3.0
Python 3.0b1+ (py3k:64417, Jun 19 2008, 21:25:46)
[GCC 4.0.1 (Apple Inc. build 5483)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import multiprocessing
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: No module named multiprocessing
>>>
After adding it to Makefile.pre.in and rebuilding/reinstalling:
$ python3.0
Python 3.0b1+ (py3k:64417M, Jun 19 2008, 22:50:25)
[GCC 4.0.1 (Apple Inc. build 5483)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import multiprocessing
>>>