Win32 - Mail & SMTP ???

I have PHP-4.0.1 running on my Win200 Pro devel box though the IIS DLL and SMTP services running. I have SMTP enabled on this machine and have outlook express configured to send mail though the local SMTP service. I simply told O.Express the outgoing mail server was my machine (just told it the machine name)..... Now to the PHP stuff .... I can't seem to get the mail function to work. A server error gets returned. I am trying to run a simple script though the PHP.EXE executable. I've tried editing the php.ini with the SMTP being localhost, my machine's name, and IP address ... I keep getting the same error. both PHP.EXE and PHP.INI reside in c:\winnt\system32 so there should not be a path problem .... any thoughts ?? thanks -j