Adding old posts to a new subdomain on multisite

Hello

I've recently transformed a single wordpress install to multisite

mysite.com/2012/10/05/love-songs/ is currently active. All outside links to it work fine.

I've created the subdomain
music.mysite.com and used the wordpress importer plugin ( http://wordpress.org/extend/plugins/wordpress-importer) to COPY my posts from the music category there.

So now I have two duplicate posts
mysite.com/2012/10/05/love-songs/
music.mysite.com/2012/10/05/love-songs/ (in maintenance mode)

So do I have to now cancel all the posts from my original music category on the main site? After which, ... will all the links to posts then automatically redirect to the new subdomain?

Thanks

Another question
P.S. Any solution to getting thumbnails and media files on the correct place on the subdomain?