I was kind of hoping that someone would have solved this by now...
I still can not use PHP pages for customizing the error pages with IIS.
All my other php pages/sites work ok but when I try to include any php in a custom error page its back to "I'm a dumb web server I don't know what I'm doing with this stuff" (or I'm a dumb admin that doesn't know how to configure PHP on IIS).
IIS 5, PHP 4, Custom Error Pages aaargh.
Cheers'
Dan