Install wordpress in a folder different to root

Settings:
– I installed WordPress 3.2.1 in a subdirectory of my root:
root/wordpress/
– I want to install my blog in another subdirectory of my root:
root/myblog/
– My domain points to root/myblog/
– I copied index.php to root/myblog/
– I set the line to
require(‘../wordpress/wp-blog-header.php’);

But it does not work.

How do I have to define the ‘require’ in order to make it work? Or how do you suggest I set up my blog instead?

Thanks so much.