I've two different blogs. Blog nr.1 and blog nr.2

I want publish nr.12 from blog nr.1 to show a hyperlink to publish nr nearest to 12 from blog nr.2. Instantly.

How do i get this to?

This is a WordPress wordpress plugin that appears to complete what you're asking about:

http://www.clickonf5.org/wordpress/wordpress-plugin-show-latest-posts-from-other-blog-feed/6480