I have a lot of broken links that are not being logged. Is there a way to setup IIS to send them through ASP.NET so that my normal 404 logging routine catches them?
You could use the host MVC on IIS 6 hack method. Basically, setup a wildcard .* mapping in IIS and have the aspnet_isapi.dll handle this request, which is the same as having .NET handle all request. You may experience a performance decrease (probably minimal), but it should hit your logging routine.