you wont be able to get the full stream of 1Gb until your switch is 1GB compatible, also, your Wires are 1Gb compatible. else you'll only get 100Mbps.
and Dual LAN comes on systems which can opt for becoming a small scall / entry level server. therefore, you can make your server as Internet gateway/ Router / DHCP server. Dual LAN is not new to Motherboards, as I remember Asus Gave Dual LAN on their A7N8X- Deluxe board for the first time, and I dont remember using both.
Intel Core2Quad 2.66Ghz 12MB L2-Cache
4096MB DDR Kingston Hyper-X
XFX 9600GT AlphaDog
Seagate 2 X 320GB SATA2
LG L246WH Flatron 24"