they have the airflow and cooling sorted out
the AMD64 is around 2 thirds the size of the 32bit proc and the CPU cooler takes up a lot of the internal space. they also have a pretty neat exhaust fan to clear away quite a bit more of the hot air. If you are worred about how many drives etc you can fit remember that it comes with firewire and usb 2.0 to front and back, couple that with the fact that external firewire/usb 2.0 external enclosures are dirt cheap you have a pretty easy sollution, either daisy chain firewire enclosures or buy a usb 2.0 hub and add drives that way. At present he has 2 external 120Gig firewire drives and a second external pioneer 108
