Setting up Multi Currency

Hi,

  Our company would like to implement Multi currency in our system. We have just one SOB and we have had it using for many years now.

  I would  like to have some guide lines on how we can set this up with existing SOB. 

 If I change the SOB definition for MRC from Not Applicable  to "Primary"  will there be any affect.

If no, then once I define a reporting currency adn SOB,  and attach it to the Primary SOB will that have any affect on the transactions that are occuring in the Primary SOB.

 Your valuable thoughts are much appreciated.