How to avoid duplicate content when I create separate site?

[Jimville]

I have a regional site. The site is primarily a directory for each of the 50+ cities in the region...by city. For marketing reasons (not seo), I am starting a seperate site for one of the cities...City A. So, the directory listings for <widget dealers> will be exactly the same for the Regional Site and the City A site....duplicate content. If I put a "no index' tag on the City A directory site, will it protect the Regional Site's directory pages?
Thanks.

[edited by: Robert_Charlton at 4:14 am (utc) on Dec. 2, 2008]
[edit reason] removed specific [/edit]

[Quadrille]

Yes; that will stop the duplication being spidered, so that only the regional site will be indexed.

I take it you will only use the tag for the listings, so other pages of the 'local' site will be able to be indexed?