just to add to the esteemed posters above, when you understand that your router is what protects you from nasties out there, and your switch helps to hand out internal addresses, then your solution becomes much clearer. hopefully, your existing router is recent.
depending upon the number of ports, buy the gigabit switch. i bought this one at memory express and i have nothing but good things to say about it. you plug in, it works:
http://www.memoryexpress.com/Product...30393(ME).aspx