How to sync the iphone 3gs with a different itunes without losing data?

i synced my iphone 3gs on a computer but now i want to sync it with my laptop now since my computer broke. How do i sync it without losing data.|||That might be difficult to do if your other computer broke. But if possible, when your iPhone opens in iTunes, check off that you want to MANUALLY put your music in and whatnot. Otherwise, it's going to automatically sync with whatever your laptop has.