Help A Dummy Set Up A Network:wacko: ? Options

[LadyWillow]

Hello I have a computer in the kitchen on adsl internet. My son has been given a new computer in his room. I would love to set up a network to share all files and internet connection but am very confused as to what I need to do this. Both comps have an ethernet adapter, xp running but the new computer is faster. I have a siemens speedstream 4200 modem which only has a usb port left unused.what do I need to get and how do I set it up? Does it matter which computer you set the network on? I also don't have a great deal of funds at my fingertips so will probably use ebay to buy what i need. Any assistance would be greatly appreciated I have read the tutorial here but still need help.I was told the modem is also a router but as it only has an usb port left I don't think this will help.