How can I map a subdomain?

Hi,

I have a website, itsbuiltforyou.com which is where my IP address points to in the domain mapping plugin. I'm trying to move things away from there and use sites.itsbuiltforyou.com as the main domain to register websites at. The only issue is when I set up domain mapping with the IP address, it goes back to itsbuiltforyou.com.

Is there a way to have this go directly to sites.itsbuiltforyou.com? Would I have to speak to my hosting provider?