do i need a router?

jus going to set up a network in my house and dont know if i need a router or not.

i have a usb modem and use windows xp. and i can share my connection with my playstation 2 wothout a router so i dont know if i will need a router to sedn information to the other computer or if i just have a wireless NIC on it, it will just work if i set it up to share the connection through the computer

No, you don't need a router - just a switch or a hub. Routers are used to share out the Internet connection within a network, but since you've already got a USB modem connected to a computer, the computer itself can share out the Internet connection (as it already does with the PS2).

To connect the computers, you'll need a switch or a hub. You'll really want to go for a switch, since they are considerably faster and not much more expensive. Each computer has full bandwidth, rather than sharing out the speed as in a hub.

If you decide to go down the wireless route, you may not need a switch or hub at all. If you create an ad-hoc network (give everything in the network a wireless network adapter), everything should be able to communicate without buying a switch/hub.

Personally, if you can, go for a wires setup, since the speeds are faster, and this will be useful when transferring files across the network.