I disable IWP by renaming the extension "Web.fmx" to "Web.fmx_DisabledByRename".
This makes it easy to re-enable IWP with a simple extension renaming.
The file is typically located at "C:Program FilesFileMakerFileMaker Pro 9 AdvancedExtensions"
As a matter of habit, I also delete FMP's web preferences file, "web.prefs".
The file is recreated by FileMaker as needed, so I don't bother renaming it.
Regards