I've found something helpful and wanted to pass it on in case anyone else is having the same problem. On this page a person indicated that adding PHP as a web service extension was a new step in IIS6. Instructions are given on that page, but the relevant step seems to be this one:
5) In IIS Manager / Your website PROPERTIES / Home Directory / Configuration add an application extension .php linked to xx\PHP\sapi\php4isapi.dll
I'm passing this info on to my admin. Not sure if it will solve the problem yet, but at least the link is useful.