You can have a wireless connection to your computer but not directly to your xbox, your xbox has to be "wired" to something.
For example, you can have your actual cable modem at one computer, and the wireless router will send the signal to another computer, but you have to use a WIRED router connect you xbox to that computer (the one connected wirelessly). But you can't have the connection sent wirelessly directly to your xbox. I have an ethernet wireless adapter, which I use for xbox live, but xbc won't let you do that. It's kind of complicated.