What need to do for supporting a new extension?

I use Ubuntu 9.10,PHP 5.3.1,apache2.24
I compiled the PHP from php source successfully.

Now I want to build the mbstring module from source. My operations:
shell> cd php src dir/
shell> phpize
shell> .configure
shell> make && sudo make install
shell> echo ectension=mbstring.so >> php.ini
Now it has built the mbstring.so.
But my php still did not support this module.

I found something in the log files of Apache Httpd server.
"PHP Startup: mbstring: Unable to initialize module
 51 Module compiled with module API=20060613
 52 PHP    compiled with module API=20090626
 53 These options need to match "

It seems so strange:
why the module APIS are different when I build the PHP and PHP modules from
the same php source tar file.

another question:
If I want to increase a dynamic module for PHP, What do I need to do?
1.setting the php.ini file
2.move the *.so files to the specified directory(extension_dir)
3.move the related headers to include directory( is this necessary?)
is this enough for finishing that task( to support a module)?
-- 
Best Wishes,
Joewan