Thanks to the work of Christian Heimes and Skip Montanaro with a supporting role by me, the 2.6 version of Multiprocessing (pyprocessing) has been forked/adjusted for compatibility with Python 2.4/2.5. You can see the pypi package here, and the google code project here.
We chose to do the back port for a variety of reasons - having the new API for the package makes it easier to jump into 2.6 if you're like me: a heavy pyprocessing user, not to mention that during the migration into python-core, a lot of bugs were fixed.
Check it out, and feel free to file bugs. We're planning on back porting bug fixes from python-core to the project, and applicable bug fixes from the google code project into python-core.