For those who want this functionality but use a version of Python older than 2.6, there is a backport of this module:

http://code.google.com/p/python-multiprocessing/

How does this relate/interoperate with stackless python? http://www.stackless.com/

It's doesn't matter. It can run with stackless/within it, and you can use tasklets. This was designed to step around the GIL, not get involved in the coroutine/tasklet/etc rats nest.