I've verified that this works correctly with the installer from the DVD, or a newer SourceForge Python for Windows project download, if you extract the contents of the installer into the site-packages folder.
Change directory into to the lib\site-packages folder and issue the command:
Or from anywhere (assuming your $PYTHONPATH variable is set)
python pywin32_postinstall.py -quiet -install
You can remove the postinstall script once finished.
python C:\Python2.6\ArcGIS10.0\lib\site-packages\python\pywin32_postinstall.py -quiet -install
You still need to deal with extracting the folder contents from the PyWin32-xxx.win32-py2.6.exe installer and deploying them to the Python2.6 lib\site-packages folder in advance of your "silent" install.
Something to consider, installing "silent" this way does not call the bdist_wininst routines that Mark Hammond uses in the PyWin32 installer. So there are no add/remove program hooks laid down, and a WISE style log of the install is not recorded. Meaning that if you later need to maintain or update the Python for Windows package you will need to manually uninstall the package and adjust registry. Not a big deal, just something to be aware of.