Ive got a DG814 netgear router mate, its a peace off piss to configure and if you need instructions I can write it down.
The router its self should be £150.00 but you can get cheap ones off the net for about £100.
Comes with a built in NAT ( networ address translator ) this takes the IP address from your ISP and seperates it into 256 private IP addresses that it gives each computer.
Its a shit hot firewall because if anyone tries to hack you they only get to the router and cant get to any PC's as the IP are all private not public.
Youll need a network card in each PC to connect them to the router. Its capable of 2 meg connection and you dont need to bother about crossed or straight cat5 cable as it detects it and you can use any you want.
Loads of gadgets port forwarding etc.
For any router your looking at about 70.00 upwads but to be honest for the extra protection + simplicity youll not go wrong with this little bugger
You can even set everything to automatic, so itllk get the IP address from the ISP for you and also it will also search for there active DNS servers as well all youll need to do is put in your account name and password supplied by your ISP.