Help needed in moving old Wordpress MU site to subdomain

I have an old version of Wordpress MU on my website to offer users the possibility to maintain a blog. As I'm renewing my site, I'm going to discontinue the blogs section. But for some months I need them to be available so the blog owners can find a new home for their blog.

The current users blogs are accessible through the URL domain.com/blogs/username (The root of domain.com points to the folder httpdocs; the blog software resides in the directory httpdocs/blogs).

Now I want them to be available using the URL blogs.domain.com/username (the root of blogs.domain.com points to httpdocs/blogs).

What should I change in the .htaccess file?
What should I change in de Wordpress MU setup (data or config files)?