Xbox360 question, transferring saved data?

I'm getting a new white xbox because my old one broke. All my old data (ex. downloaded map packs for COD) were saved onto my hard drive and i want to move that stuff to the new white xbox that im getting. Both white xboxs are the exact same model and they both have the same hard drive i believe. I was wandering if i recover my gamertag on the new xbox; will all my save data like the mappacks be there again, or do i have to get a usb thing and put everything on there and move it? i hope somebody understands me.