I, too have failed miserably.
Webinator works fine without the ISAPI but we liked it and had successfully installed on a win 2000 Advanced Server and on a Win XP Pro machine with no problems.
But we have tried to install it as part of the install and after the install on two Win 2003 Web servers and we cannot get the filter to run.
Within Web Extensions we have specifically allowed both .exe and the Texis ISAPI but with no joy.
It seems definitely to eb an IIS6 permissions issue but I am baffled.