Maybe this'll help a bit.
http://s93744050.onlinehome.us/PalmMute.mp3

Here I'm playing an open A chord and gradually bringing the palm of my right hand down over the bridge of the guitar so they start to sound muffled.
The more you raise your hand the clearer the sound gets.
Eventually you get to the point where you're using it like the dampening pedal on a piano.