API FAQ from PHP3 to PHP4

Is there an FAQ or quick start on the things you need to do to port an extension from php3 to php4? I've looked all around php.net and zend.com for info and have come up short. It looks like it should be straight forward. I've included the php3_compat.h, and adjusted the headers. Everything compiles and links okay. When I go to load the module using dl("libpasswd.so") in php, I get this error. I haven't been able to figure out what this API= means, why it's significant, or what I should do about it. Any help would be appreciated. Please reply via email as I'm not currently subscribed to this list. Warning: CRACK: Unable to initialize module Module compiled with debug=0, thread-safety=0 module API=0 PHP compiled with debug=0, thread-safety=0 module API=20000809 These options need to match in /var/www/imapssl/passwd.php3 on line 123