Two networks on the same pc?

Does anyone have any experience with, or know how I could, setup a home network where I could achieve the following without using a hub?
Computer A has broadband internet access and is connected, via 100Mbps ethernet cable, to computer B. Computer B is then, via a USB wireless network card, connected to computer C, a laptop also with a wireless network card. All computers are running Windows XP.
I am not sure if this will be possible without a hub, but does anyone have any suggestions?

Look into enabling packet forwarding on computer B, depending on the OS. Also, router software could be installed on computer B. You can buy a 5 port 10/100 switch for US$25-30 if you need to anyway.