PHP ISAPI Filter on Windows 2K

I am trying to bring PHP 4.1.1 up on a Dell Poweredge 1500, running Windows 2K, SP2 and IIS 5. I have it running on an almost identical test machine right beside it. However, when I try to restart the server, the ISAPI filter fails to load, and I get a message in the Event Viewer saying - Source: W3SVC Category: None Type: Error Event ID: 14 User: N/A Description: The HTTP Filter DLL C:\WINNT\system\php4isapi.dll failed to load. The data is the error. For additional information specific to this message please visit the Microsoft Online Support site located at: http://www.microsoft.com/contentredirect.asp. I have the php4isapi.dll file located in the winnt/system directory (Although I also have a coopy in the system32 directory and I get the same error) I have copied all of my .dll's from the php/dll and php/extension folder over to both the system and system32 directory and have the php.ini file in the winnt directory. For now I have installed it as a cgi, but I've been told there are a lot of speed benefits gained from running as an ISAPI filter. Can anyone help me out, or set me straight if I don't need ISAPI? Thanks! Zack