Get a speaker similiar to these:
http://www.bose.ca/controller?url=/s...on_3/index.jsp

You want a pair of speakers that have an AUX Input so that you can use them as computer speakers AND plug an external source such as an ipod or in your case an xbox 360.

Running out of these AUX input would be this Y Adapter
http://www.memoryexpress.com/Product...X6019(ME).aspx
And thats where your red and white from your xbox audio plugs will go to.