Moving a WP install from root to a subdomain and replacing it with a new site

Hey all,

I have a domain with a large WP installation in the root directory. It is the latest version and uses buddypress as a content management system. I have a network setup and have several simple Wp installations under subdomains. Here’s what I’m trying to do:

I want to take the huge current installation that is in the root directory and move it into a subdirectory (accessible by a subdomain like all the rest of the sites in the network) and replace it with a simple WP installation. I have tried changing the URL’s and then copying all the files to the subdirectory and redirecting it to a copied database, but it just gives me a database connection error and when I delete the config file and start a new one, the site looks ALL screwed up.

Is there an easier way to do this that I’m missing?

Thanks