My hard drive and Duet are both FireWire, but I only have 1 FireWire port on my computer. Can I connect the Duet to the hard drive or a FireWire hub?

Yes, if you have a Firewire Hard drive or hub with two Firewire ports, then the Duet can be connected to the 2nd Firewire port on that device. Though this is not recommend for data-hungry devices, as it may overload the firewire bus causing audio stability issues.