For the brave enough to run a 64-bit Python under a 64-bit Windows installation, I have added a first version of ctypes for win64 in the sourceforge download area. It does NOT use the same sourcecode as the 'official' version, the code has been patched by merging selected commits from the Python SVN trunk.
This release is not too much tested; in fact even one unittest still fails. The failure only occurs when compiled for Python 2.5 with the MS SDK compiler, not with Visual Studio 2008.
If you try to use ctypes-win64, be sure to use the proper argtypes and restypes attributes for dll-functions; integers (which ctypes assumes by default) and pointers have different sizes on 64-bit Windows.
Apart from that, enjoy.