The main problem with this is even with gigabit cards on each PC, as well as decent Cat6 cable, a router to share you internet connection will not run gigabit.
You'll need to get a seperate router to handle your NAT and DCHP duties, or a dedicated linux router. Then use a gigabit switch to connect all you machines to each other and uplink the switch to the router.
The cheapest that I can find would be the Linksys EG00SW found here:
http://www.compusa.com/products/prod...271&pfp=BROWSE
You'll want to be sure that you'll use the high speed of the gigabit equipment before investing this kind of money in a system. If you transfer a lot of files between machines, it will help a lot, but only to the point of the transfer limit on your HDD.
EDIT: D-Link also makes a similar switch that is slightly less expensive here:
http://www.shipitforyou.com/cgi-bin/...04071412404273