Julie,
Well it depends on what the budget is and the kind of perfomance that is required. Iomega makes a NAS that is RAID 5 and fairly inexpensive (as far as NAS devices). They also come with dual ethernet interfaces that can trunked and usually depending on the model will come with a gigabit port. If the budget does not allow for this then the previous sugestions would be good..... building a PC with a SETA RAID controller.