I'm actually in the process of using this...unfortunately I'm out of com ports, and the pci serial card I thought was in working condition isn't...so I have to replace it...any way, I wired a relay to the serial port so that when the relay is on, it pushes button 1 and holds it, and when it's off it pushes button 2 and holds it. The relay is triggered by the ACC line. Both buttons pause winamp.
The purpose of this is that when I stop the car, it pauses the music, and when I start the car again, it unpauses the music. Tested it on my laptop, works great.