Cheapest way to get Xbox 360 online wirelessly

FWIW, here's the little wireless adapter that's been working for us for about a year - a little cheaper, easy to set up, no hassles. Not sure I'd have the patience to boot & attach the laptop every time I wanted to use the xbox.

You should be able to do this for free. Follow the instructions here:

• How can I connect my Xbox 360 to Xbox Live through my Laptop?

The instructions are for how to use a wifi laptop as a wireless adapter for the XBox, but they should work for your media center PC as well.