CPU : Core i7 2600 (or a Quad Core Xeon)
RAM : 16GB DDR3 Buffered Ram
Hard Disk : 2 x 500GB In level 1 Raid for Operating System; 2 x 2TB in level 1 RAID for Data and sharing
LAN : 10GBE network speed (if you cannot do that, go with 4 x 1gb/s ports)
Get yourself a nice UPS and Switches.