Speech Recognition
There are two significant Speech Recognition Engines:
Nuance DNS - Nuance Dragon Naturally-Speaking
Dragon Naturally-Speaking is a high quality commercial product
available (at a price) from Nuance UK.
Microsoft WSR - Windows Speech Recognition
Windows Speech Recognition is included in Microsoft Vista
or is available as a free download for Windows XP.
A user interface to Microsoft speech software can be written as a Python module.
More about Microsoft WSR
Dragonfly is a speech recognition framework.
It is a Python package supporting both the above engines.