router or switch?

Router's join two or more networks. In the market your talking about it's usually two networks, yours and the internet. Takes a public IP address and uses NAT or PAT with an internal IP scheme (192.168.x.x etc..) to distribute the broadband or dialup connection. If your concerned about worms, trojans and hacking in general then you'll be staying with the router, not to mention most broadband providers will charge you for each additional IP, so if you used a switch each computer connecting to an uplink switch from the cable modem would get a WAN IP from the ISP, thus an additional charge for each PC.

Nope, no gigabit routers that I am aware of. If you want gigabit connectivity from desktop to desktop then buy a gigabit switch, one that is 100/1000 at least to the uplink and uplink that switch from your router's switch, then hook your PC's into the gigabit switch. Your internet connectivity would still come from the router but your internal network would transfer files, streams etc... at gigabit speeds. Well, if your disk subsystem can take advantage of it. Gigabit, while not completely worthless, is more than all but the most advanced home networks needs. You won't see mind boggling performance increases by going gigabit, especially unless you have something like striped SATA Raptor hard drives in your PC's. Or quick SCSI disks in a striped RAID configuration.