Xbox / desktop/ wireless question.

Hello,
My stepson has an xbox and plays xbox live online using our wireless system. We have given him a used computer and he wants to put it in his room to surf the internet but it doesnt have a wireless card in it. Can whatever causes the xbox to receive the wireless signal somehow cheaply be used to cause the desktop computer to receive the wireless signal as well? If not what are our options? There are no phone jacks in his room so conecting THAT computer directly to the DSL isnt really an option.

Any ideas here?