I just bought the same monitor as you. It arrived yesterday, and I've set it up with my PC and 360 today. If your 360 has an HDMI port, all you need is an HDMI-HDMI cable. Since HDMI handles both audio and video, all you need to do is connect any speaker or headphone into the back of the monitor (not your PC) and it works great. I had to register and reply, seeing as the other 2 replies as being more complicated than I suspect you require.

Edit: Apparently I can't tell June from July. I guess I'm a month late.