Wow this is cool!
http://www.2loop.com/hsound.html
This is meant to be listened to on headphones, but if you don't have headphones, just take your 2 desktop speakers and hold them up to your ears, close enough that each ear will only hear the sound coming from their respective speaker.
If you've got 5.1 surround or something fancy, sorry, but you're out of luck and thus won't get the effect.
If you DO have a working setup, I'll just say wow! ....it totally sounds like someone is really behind/in front of you

Really creepy...they should (somehow) use this in movie theatres!