I installed ActivePython 2.7 on the WinServer 2008r2. Activepython 2.7 comes with pywin32. The use of ISAPI package fails with error 500.0. THe IIS failure page is at http://snag.gy/33FuZ.jpg
I have verified with dumpbin that the PyISAPI.dll that comes with the package is indeed x64 version.
I worked around this problem by installing x86 activepython + pywin32 on the same machine. And let IIS to load 32bit applications.