Absolutely. Just look for an RCA splitter. Talk to one of the reps at teh store. Also ask them if they have a 3.5mm Splitter/Switcher so that you can use a normal 3.5mm cable out from your computer and just buy one Female RCA to Male 3.5mm cable to your splitter and plug your headphones right into it.
I was a little incorrect above. The cable you see in the picture needs to be MALE RCA to female 3.5mm jack so you can plug in your headphones to it and plug the male RCA into the output on the splitter.
SORT OF what your layout should end up being like:
You will need the single RCA video cable because of the Xbox360's cables. You can't separate the video from the audio UNLESS you are using the component video. If you are using component video, you don't need the single video cable.