Creating DLL files for PHP4

I want to take some C code and create a dll file that will be interpreted by php 4.0.x as a php library (i.e. php_myphplib.dll). What I need to know are the steps taken to make the library recognized by php in both the dll definition and implementation. I have downloaded and tried to use libmcrypt.dll which is supposed to implement the mcrypt functions. I have tried dl("libmcrypt.dll"); and extension=php_mcrypt.dll and I get the following: Warning: Invalid library (maybe not a PHP library) 'libmcrypt.dll' So, I know there is something specific to the dll file that allows it to be interpreted by php. Any information such as a tutorial, tips, examples, or anything would be great. Thanks, Jay Paulson