Access to wordpress admin in sub-directory of new build?

I have my 2.9 wordpress site running and want to build a brand new site with 3.0 in a sub-directory called /wordpress.
I uploaded wp 3.0 and the new theme I have been working on and also took the root wp-config file and copied this into the sub-directory wordpress 3.0.
But I cannot access the sub-directory admin pages to change the URL.
Anyone know how this works? What is wrong here…?
Thanks.