Trouble with IIS 5.0, Win2k Sp3 and PHP 4.3.1 - Modules not found

I am using a fresh installation of PHP 4.3.1 on a Win2k SP3 machine with IIS 5. I am having a heck of time getting any of the included PHP extensions to load during IIS startup. I am consistently getting error messages like: Warning: Unknown(): unable to load module 'c:\php\extensions\php_mssql.dll' - the specified module could not be found. Now, I have my php.ini file set up correctly in that the extensions dir is specified as c:\php\extensions. The files are there - I can open up a cmd window and list them no problem. What's more, I have another W2k SP3 IIs5 box that also has PHP installed and it seems to pick up the mssql module without errors. I have looked at permissions, I have fiddled with moving the dll's around into \winnt and \winnt\system32, etc. I keep getting this error. The fact that it seems to be working fine on another machine is baffling and frustrating. Any ideas? -Will