I would use a gigabit networked NAS box with the computers connecting to the mapped network drive. If you router doesn't have gigabit LAN ports, just add an inexpensive gigabit switch.
If you want to save some money and one of your computers has the space, you could put the drive or drives into it and share the drive over the gigabit wired network.
How large are your storage needs and is the setup primarily for data storage?
Each of the external drives are 2 TB Hartachi SATA III. All of the internal bays are full and all of the internal SATA ports are in use. The drives are used to edit and store video from travels.
As part of this question if I got a unit that has both USB3 and ESATA could the USB3 be connected to a USB3 port on the Vista box with a GiGabyte GA-P35C-DS3R which does not have the capability to see more than one drive when using eSATA and the ESATA connector connected to the Windows 7 pc whose ASUS P6T board does see both drives in the Therrmaltake 2 drive unit? Since i am moving accessing files that are very large ie 20 GB each I would not like to use my wired gigabit switch.