If you had purchased the latest/greatest Redhat Enterprise, there might be some fancy migration tool and/or an "officially recommended procedure".
But since you're on Centos (Centos 5.5), just pretty much choose whatever procedure most appeals to you, and post a new thread with any specific questions you might have or problems you might encounter.
IMHO .. PSM
My dog ("Scamps") is *black*. And she's waiting for a walk. Gotta go