Release 305
You should use pip:
pip install pywin32 --upgrade
.exe installers are now deprecated, but while they still exist, you must choose both the correct Python version and "bittedness". Even if you have a 64bit computer, if you installed a 32bit version of Python you must install the 32bit version of pywin32.
There is one binary per-version, per-bittedness. To determine what version of Python you have, start Python and look at the first line of the banner. Compare these 2:
Python 2.7.2+ ... [MSC v.1500 32 bit (Intel)] on win32
Python 2.7.2+ ... [MSC v.1500 64 bit (AMD64)] on win32
^^^^^^^^^^^^^^
If the installation process informs you that Python is not found in the registry, it almost certainly means you have downloaded the wrong version - either for the wrong version of Python, or the wrong "bittedness".
But as above: .exe installers are deprecated - please use pip.