If you still receive 404 errors... try this...
I had to:
1) right click on My Computer, select Manage
2) open up "Services and Applications" -> "Internet Information Services" -> "Web Sites" -> mywebsite (where mywebsite could be "Default Web Site" or whatever my web site is named)
3) right-click on mywebsite and select Properties
choose the "Home Directory" tab, select Configuration... button
4) either select the .php extension and choose the Edit... button, or if .php isn't listed then press the Add... button
5) make the Executable C:\WINDOWS\system32\inetsrv\fcgiext.dll, the extension .php, and ensure Verbs are limited to GET,HEAD,POST, check the "Script engine" and "Verify that file exists" check boxes
Once I did this I at least now get the 500 fastcgi error