If you go to the Media page on the dashboard, if you look at one of them ( I cant remember which,just look at all of them) it will give you instructions on what to do. You will need to download the latest windows media player and will need to set something up. this is quite complicated, so you will probably need someone else to help you, but once you have done it, on your 360, look at some files in videos or music etc. and press X. Press A on the one which is what your computer is called E.G. "Administrator"
Now you will be able to view your music and video files saved on your PC.
If you the Xbox live arcade maker then you can open them up too.
Hope this helps!
Yay first post! ;-)