PHP start up cannot find the extensions

I have installed PHP 5.0.2 from the installer off of php.net running on 
Windows XP Pro with the IIS server stuff installed.  I know that it didn't 
come with the external extensions so I downloaded the full zip file and 
copied the dlls into the following directory:

C:\PHP\ext

Then I opened php.ini in C:\Windows and changed the extension_dir command to
extension_dir="C:\PHP\ext"

Then I uncommented out the php_mysql dll in the list of extensions.  Despite 
having done all of this I still cannot get php startup to load my extension. 
I get the error:
PHP Warning: PHP Startup: Unable to load dynamic library 
'C:\PHP\extensions\php_mysql.dll' - The specified module could not be found. 
in Unknown on line 0

I can browse right to php_mysql.dll using the exact path that it gives me in 
the error message.  Any ideas what is wrong?

thanks,

Danny