Repeat after me:
Firewire. Firewire. Firewire. Firewire.
When you select an external drive, don't believe ANYONE who tells you USB2 is virtually as fast as Firewire. USB2 burst speeds are fair, but for steady throughput of large volumes of data, USB2 is pathetically slow compared to Firewire. I recently bought a USB2 Western Digital external drive, much vaunted for its reliability. Biggest waste of money ever compared to my other Firewire drives.