I think you mean .pyc (or .pyo) rather than .pyd (which is used for DLLs used as Python extension modules on Windows).
I've heard that it is pretty easy to decompile them back into .py files.
You could compile them with Pyrex, and then you really would have .pyd files (or .so on Linux). :-)
You'd have a somewhat harder time decompiling those back into .py files...
-- Greg