How can I make the button on my headphones control something other than the stock music player? When I press this button, it plays/pauses the stock music player. I don't use the stock music player--I use a comination of Last.fm, Grooveshark, and Winamp. I would like to make the button play/pause whichever player I am currently using. If this isn't possible, I would like it to simply control Winamp, instead of the default player.

I am using Android 2.1 (unrooted) on a Samsung Fascinate.
To get the headset to control only one application:

The application has to support receiving headset control events.

In the case of Winamp, press menu --> Settings --> Enable "Control headset"

If there are multiple apps that accept headset controls, you may have to disable the feature on the other apps (I'm not certain which app gets priority over another).