installing extensions

I'm trying to install php 5.0.4 with Apache2 in directory

c:\php-5.0.4-Win32

I set extension_dir = "C:\php-5.0.4-Win32\ext" in php.ini

I uncomment extension=php_mysql.dll

Restart Apache and I get the error message

PHP Startup: Unable to load dynamic library
'C:\php-5.0.4-Win32\ext\php_mysql.dll' -the specified module could not
be found

but it is there... Am I doing something stupid?

Read the manual, it talks about this:

http://php.net/mysql

I have. I should point out that *any* extension I try to load gives me
the error. I've tried every slash combination. The path displayed in
the error is the correct path. This should be a no-brainer. (maybe
that's the problem, maybe I got no brain???).