My route is not cheap. My set up is Xbox360 via VGA cable plugged into a Avermedia TV Box (
http://www.aver.com/mpd/tvbox7.html), and VGA output from it to my PC monitor. That device has both VGA input to receive your 360 and VGA output to your PC monitor, and it also has an input for your PC speakers for audio. Shop around online to see if you can find a good price for it.