Thanks for the tip about the mscoree access being unimportant. It turns out the pywin32 installer works fine with win2K set, but that doesn't help Twisted_NoDocs-8.2.0.win32-py2.6.exe, which still fails to find win32api. However, if I install ActiveState's python instead of the one from python.org, twisted installs successfully.
Now on with the buildbot experiment :-)