Transfering content between domains (effect on google)
 

I will be switching to the vbulletin suite soon. With the new CMS want to change the structure of my site.
My website & forum are not a whole (different layout, no integration) I want to change that..

There is some popular content on my site that gets a lot of traffic from google. I want to relocate that content to an other domain.

What is the best way to do it?
Relocate content from domain 1 to domain 2. Make a redirect from domain 1 to domain 2?

Anyone have some tips?