By everything you mean all their data ? Or operating system/applications/whatever too ?
Generally speaking and method for copying data is fine. But I'd recommend reinstalling applications from scratch: depending on how you copy sommetimes hidden files can get left behind. Data files are fine though. Use a DVD sure, or a flash drive, or you can even link the two computers together as a network and copy things across, but that's a bit more complex. Copy from old, and then copy to new.
Or there are applications that creates back-up disks for you to restore elsewhere.