Domain Mapping Help Please

I host with Media Temple :

I host a few domains here:

ie, those domains point to nameservers : etc

Now.... is wpmu, buddypress
subdomains work, eg:

What I want is to close down (old Wordpress site) and create this site at

I installed the plugin.
Set custom domain to (Original name =

Now what happens is redirects to which doesnt exist (ie, it shows my root site which is

How do i get it to show the site configured on