WP Domain Mapping

Hi,

Is it possible to do this with WP 3.0:

On domainA.com I have WP installed with network enabled with subdomain. I create a new blog on subdomain (blog1.domainA.com). Then I will map this new blog (blog1.domainA.com) to appear on blog.domainB.com. Is this possible, and how can I do it? Do I use Aname or Cname or DNS or something else?