360 Knows to automatically switch to crossover, I do it occasionally on the missuss old PIII Dell Laptop.
made up a cross over cable for it and couldnt get it going
chopped crossed over connector off and it worked spot on, bizzare eh?
just a quick note, highlight the two network adapters, the one you use for pc network and then the lan port the xbox is in and right click and bridge them.
xbox will then just use your wireless as if pc isnt there.
ran my xbox like that for the past 2 years, got bored of having to have pc on though so just connected it straight to the hub now on its own cable.